XIV. IMMUNITY ACQUIRED BY NATURAL MEANS…

XIV. IMMUNITY ACQUIRED BY NATURAL MEANS

Immunity acquired after recovery from infective diseases.—Immunity acquired in malaria.—Humoral properties of convalescents from typhoid fever.—Preventive power of the blood of persons who have recovered from Asiatic cholera.—Antitoxic power of the blood of persons who have recovered from diphtheria.

Immunity acquired by heredity.—Absence of hereditary immunity properly so-called.—Immunity conferred by the maternal blood and by the yolk.

Immunity conferred by the milk of the mother.

[Sidenote: [454]]

It has long been known that an attack of one of many of the infective diseases brings about a refractory condition of the organism against that disease, a condition which persists for many years, and may even endure for life. Even before the microbiological era of medical science had arrived it had been fully established that a person who had recovered from small-pox might come in contact with and nurse small-pox patients without risk of contracting a second attack of the disease. The same thing has been observed purely empirically in several other infective diseases, such as whooping-cough, typhoid fever, scarlatina, mumps, etc. On the other hand it has been shown that certain infective diseases, such as fibrinous pneumonia, erysipelas, recurrent fever, and influenza, do not leave behind them the slightest trace of an immunity. It has often been observed, indeed, that after a first attack of any of these diseases there is a marked susceptibility to a second attack. Between these two extremes come the infections which are followed merely by a refractory condition of shorter duration than that which follows the diseases of the first group. The first of this intermediate group is measles, which gives rise to a relatively long immunity, then come in order bubonic plague, anthrax, cholera, etc.

[Sidenote: [455]]

It should be stated that the first attack of any of the infective diseases causes modifications more or less permanent in the organism, and is always followed by immunity. Even in erysipelas, a disease where the relapses are so frequent that certain individuals are, so to speak, predestined to re-acquire it at short intervals, an immunity is produced, but a very transient one. Since the discovery of the streptococcus of erysipelas by Fehleisen[724], this observer, and several other investigators, have inoculated it into persons affected with malignant tumours. In the course of a series of experimental cases of treatment it was noted on several occasions that after a first inoculation, followed by typical erysipelas, a period of immunity was developed, during which the introduction of the streptococcus produced no result. It has also been observed that recurrent fever, when inoculated into monkeys, sets up a very transient but real refractory condition. In fibrinous pneumonia, also, the relapses are generally separated by periods of immunity, of longer or shorter duration.

[Sidenote: [456]]

It was generally supposed that an attack of malarial fever was not only not followed by any immunity, but that a first attack predisposed the organism to a second. Facts of this kind have often been observed and cannot now be questioned. Nevertheless, an acquired immunity against malaria is developed under certain conditions. During his travels in New Guinea, Koch[725] found that in certain regions whilst most children below ten years of age are attacked by malaria, and Laveran’s parasite can be demonstrated in their blood, older children and adults are completely immune from this infection. Koch is convinced that in this instance we have an example of immunity acquired by natural means as the result of an attack of malaria at the younger age. This great observer bases his conclusion on the fact that unattacked adults, coming from districts where the children contain the parasite, do not contract malaria when they migrate to other malarial regions, whilst natives coming into these same regions from districts where malaria does not exist are soon attacked. Max Glogner[726] has attempted to explain these facts established by Koch, on the assumption that the unaffected adults simply benefit by their natural immunity and that we have here a kind of selection: the adults who are susceptible to malaria die as the result of this disease, whilst others, naturally refractory, resist and show themselves incapable of contracting the disease even in other malarial regions. Glogner in support of his view cites the case of the children of the orphanage at Samarang (Java), who for many years are subject to relapses and to malarial re-infections and are incapable of acquiring the slightest immunity. According to Koch, Glogner’s example cannot be compared with that of the children of New Guinea. In the former case, the natural course of the disease is interrupted by treatment with quinine, which must prevent immunity being set up; whilst, in the latter, the children are abandoned to their fate, and, receiving no treatment, slowly acquire a true immunity. It is evident that this acquired immunity in malaria is a complex phenomenon on which fresh researches must be made; but it cannot be questioned that, under certain conditions, it comes under the general rule and can be naturally acquired.

This general rule is that, in infective diseases, immunity is usually developed after a first attack. The acquired refractory condition is of very long duration in certain cases, but very transitory in others. To the discovery of the vaccination by attenuated micro-organisms, made by Pasteur and his collaborators, the objection was often made that many diseases, such as anthrax, might relapse. This is undoubtedly the case; the anthrax bacillus may attack the same individual several times; nevertheless the acquired immunity against this disease is very real, though the refractory condition lasts for one or a few years only, instead of persisting for a very much longer period, as in the case of typhoid fever, mumps, and small-pox. Bearing in mind the possibility of a relapse in the case of these infective maladies, attempts at artificial vaccination should never be relinquished.

[Sidenote: [457]]

Among the examples of immunity acquired by natural means must be cited that of syphilis, a very special case. It has long been known and demonstrated by numerous experiments on man, that individuals who have presented the primary symptoms of syphilis contract a marked immunity against a new infection. The syphilitic chancre does not relapse, and yet this very manifest and persistent immunity does not prevent the individual, immune against re-infection, from continuing to be ill and of being the field for the later syphilitic phenomena. This special refractory condition has done great service in establishing the etiology of certain diseases which we were justified in suspecting to be of syphilitic origin. Many clinical observers have accepted this origin for general progressive paralysis. Others deny any causal relation between the two diseases. Krafft-Ebing[727] has resolved this question by the application of the law of acquired syphilitic immunity. The inoculation of the syphilitic virus into ten persons attacked by general paralysis was followed by no chancre at the seat of inoculation and by no other primary or secondary symptom of syphilis. The patients with general paralysis present a real immunity against these symptoms; consequently general paralysis is a tardy manifestation of syphilis.

The acquired immunity against re-inoculation by the syphilitic virus is established immediately after the end of the period of incubation of the first infection, and is of lifelong duration[728]. Besides this very special and, so to speak, partial immunity, there exists in syphilis a second form of acquired immunity which is of a more general nature. According to the law known as the law of Baumès-Colles, the mother who suckles her infant, hereditarily infected with syphilis through the father only, enjoys a real anti-syphilitic immunity.

[Sidenote: [458]]

In tuberculosis the few facts of acquired immunity that have been observed present a certain analogy with those bearing on immunity in syphilis. A large number of well-observed facts demonstrate that a person who has suffered from scrofula or has manifest symptoms of tuberculosis properly so called, cannot count upon an immunity against pulmonary phthisis. It might, then, be supposed that no acquired refractory condition exists in connection with this disease. Koch[729] has clearly demonstrated, however, that tuberculous guinea-pigs, into which the bacilli of tuberculosis have been introduced subcutaneously, react against these bacilli in a very special manner. The presence of these micro-organisms immediately sets up an active inflammatory process at the point of inoculation; this brings about the expulsion of the bacilli with the exudation; a voluminous slough is developed, which, when shed, carries with it a large number of bacilli, a process followed neither by the formation of a permanent ulcer nor by hypertrophy of the neighbouring glands. As in syphilis, the animal has acquired immunity against re-infection by the tuberculous virus, which, however, in no way prevents the first inoculation from becoming generalised and setting up a fatal tuberculosis of almost all the organs. Koch’s observations, which have served as the basis of his researches on tuberculin, have been confirmed by other investigators. The reaction of the tuberculous organism against re-infection has received the name of “Koch’s phenomenon.”

Clinical medicine has afforded many data of the highest importance bearing on the establishment of an acquired immunity in many infective diseases; but a scientific study of the mechanism of this immunity could only be founded on the result of microbiological researches obtained during the recent period of scientific activity. The general conclusion to be drawn from these researches is that the immunity, acquired by natural means, is very analogous to that which is obtained artificially by vaccination by the various methods already mentioned. The phenomena observed in animals inoculated with the various known vaccines present a great resemblance to those that obtain during recovery from a disease contracted under natural conditions. To support this thesis it would be necessary for us to survey the mechanism of healing, which would carry us too far afield, the subject being far too vast to be summarised here. We must, then, content ourselves with a few remarks inserted for the instruction of the reader on this subject.

Those diseases against which no remedy exists are most suitable for furnishing us with important information on immunity acquired by natural means. We have already seen in the case of malaria to what point therapeutic treatment can modify the natural course of the phenomena. For this reason it will be useful to consider first the immunity acquired as the result of a first attack of typhoid fever. The immunity which develops in this example is both marked and persistent; the therapeutic intervention which might disturb the natural phenomena is nil.

[Sidenote: [459]]

As yet we do not know the mechanism of healing in typhoid fever. This disease affecting the human species exclusively (the experimental peritonitis of animals, set up by the typhoid coccobacillus, is distinguished by very marked differences), it is very difficult to find a means of studying it at all satisfactorily during the phase of recovery. Even in default of this knowledge, however, it is possible to gather some idea as to the changes which the blood plasma undergoes, not only during the course of an attack of typhoid fever, but also during and after convalescence.

Some time ago Chantemesse and Widal[730] observed that the blood serum of persons attacked by typhoid fever acquires the property of inhibiting the experimental peritonitis set up by the typhoid coccobacillus in laboratory animals. The blood of the patient becomes “preventive.” Against this conclusion the objection has been raised that in the large doses of serum employed by the above observers a protective effect can be obtained, even when using the blood of normal men, i.e. neither suffering from typhoid fever, nor having recovered from this disease. Later researches, however, have confirmed the observation made by Chantemesse and Widal. It is no doubt true that the injection of half a cubic centimetre of normal human serum into the peritoneal cavity of an untreated guinea-pig is often sufficient to render it refractory to a dose of typhoid coccobacilli fatal to the control animal. We have an ordinary protective action, such as described in Chapter X. The blood of typhoid patients is, however, capable of protecting normal animals, in doses which exhibit not the slightest protective action if normal blood be used.

[Sidenote: [460]]

The protective power of the blood serum of convalescents has been studied very carefully by Pfeiffer and Kolle[731]. In certain individuals very small quantities (0·001 c.c.) of this fluid were quite sufficient to confer on guinea-pigs an immunity against fatal typhoid peritonitis. This power was at its maximum only during the first weeks of convalescence. In one case, in which these observers were able to study the properties of the blood on two separate occasions, they found that two months after the first examination there had been a marked falling off in the acquired protective power. In a second case, where the blood was examined a year after the patient had recovered from a grave attack of typhoid fever, they found only feeble indications of this specific protective property. “Everything seems to indicate,” conclude Pfeiffer and Kolle, “that the protective typhoid substances were rapidly eliminated by the blood stream. If further researches should confirm these results, as yet few in number, we might conclude therefrom that the immunity which, after an attack of typhoid fever, persists for years, frequently even for the rest of life, would be independent of the amount of ready-prepared protective substances in the blood” (l.c. p. 218). The facts upon which this conclusion is based confirm the general thesis that even acquired immunity is in no way the function of any humoral property.

We know that in the protective serums there is constantly found the specific fixative (the sensibilising substance of Bordet, the intermediary body or amboceptor of Ehrlich). It was, therefore, quite natural that this substance should be sought in the blood of patients who were suffering, or had recovered, from typhoid fever. Bordet and Gengou[732] easily demonstrated, by the method described in Chapter ix, the existence of typhofixative in the blood serum of two individuals convalescing from this disease.

Widal and Le Sourd[733] extended this discovery to the blood taken during the course of the disease from typhoid fever patients. The ten cases studied by them all gave a positive result, whilst all the samples of blood from persons suffering from various other diseases possessed no typhofixative. As yet we do not know whether this substance persists for any length of time after recovery or not. In this respect we have much more information concerning another humoral property of typhoid patients,—specific agglutination. Guided by the fact that, even during the course of the disease, the blood of persons suffering from typhoid fever acquires protective properties, Widal sought to find out whether the agglutinative power of the fluids of the body appears equally early. We know that his studies gave a positive answer, and that the blood of typhoid patients may have agglutinative properties from the first day of the disease. This fact was made use of by Widal to establish the serum diagnosis of typhoid fever, a method now generally used in clinical medicine. The question which most interests us at this moment is whether this acquired agglutinative property persists for any length of time after the recovery of the patient, and whether it can be employed as the measure of immunity obtained.

[Sidenote: [461]]

In certain cases the serum was found to be fairly strongly agglutinative for a considerable period after recovery had taken place. But these cases are rare, and the agglutinative power, like the protective power of the blood, usually begins to decrease very soon after recovery. Bensaude[734] observed that the former disappeared between the 10th and 95th day of apyrexia. Widal and Sicard[735] have noted in certain of their cases the complete disappearance of the agglutinative power of the blood, which took place in one case on the 18th, in another on the 24th day of defervescence. In many convalescents, fifteen to thirty days after the commencement of apyrexia, the agglutinative power begins to be attenuated.

Previous to these researches on the protective and agglutinative properties, Stern[736] had already put the question: May we not draw some general conclusion as to the bactericidal power of the blood serum of convalescents from typhoid fever? He found that the typhoid coccobacilli did not thrive so well in the blood serum of persons in good health as in that of convalescents, in which they give abundant cultures. Widal and Sicard (l.c.) subjected this question to a fresh examination, and showed that in this respect there exists no constant or marked difference. Thus, in ten samples of serums from individuals who had never been under the influence of the typhoid infection, four were found to be bactericidal for the typhoid coccobacillus. In twelve other samples, drawn from convalescents from typhoid fever, five exhibited a bactericidal power against the same micro-organism.

All the researches made on acquired immunity after recovery from typhoid fever demonstrate clearly that, in this case, it is impossible to attribute it to humoral modifications, which are usually more transitory than the immunity.

[Sidenote: [462]]

The immunity which follows an attack of cholera is far from being either as powerful or as prolonged as that which follows typhoid fever. Certain individuals have contracted cholera twice during the same epidemic, but such cases are exceptional, whilst acquired immunity, temporary at least, may be looked upon as the general rule. Many points in the pathogenesis of intestinal cholera are still obscure; nevertheless we are justified in affirming that this disease is a real intoxication by the cholera poison manufactured, in the small intestine of man, by Koch’s vibrios. The action of the vibrionic toxin is sufficient to set up a grave and often fatal attack of cholera; but in the majority of cases a secondary infection by the vibrio which penetrates into the intestinal wall, denuded of its epithelial layer, is associated with the action of the poison. Sometimes this micro-organism becomes generalised in the animal, and is found in the blood and in many of the organs.

The facts I have here briefly summarised may be utilised to explain certain characters which are found in the fluids of individuals who have recovered from an attack of cholera. Soon after the discovery of the tetanus and diphtheria antitoxins, and almost immediately after the demonstration of the protective power of the blood, taking advantage of the epidemic of Asiatic cholera, which developed in Europe from 1892, the new data began to be applied to that disease. We have already referred in a preceding chapter to the fact that the blood serum or the blood of those in good health and who have never had Asiatic cholera, is capable of preventing cholera peritonitis in the guinea-pig inoculated with Koch’s vibrios. In order to obtain this protective action, the injection of a pretty large dose, about half a c.c., is necessary. This property is in no sense specific, for the same blood, injected in the same doses into guinea-pigs, will protect them not only against this vibrio, but also, and indifferently, against many other bacteria, such as the typhoid coccobacillus, the Bacillus coli, etc.

The blood or blood serum, coming from those who have recovered from Asiatic cholera, may, on the other hand, acquire a specific protective power. It will, indeed, prevent infections by other micro-organisms; but, to obtain this effect, it is necessary to inject the same quantities of it as of the blood coming from normal individuals. On the other hand, when we wish to prevent cholera peritonitis in the guinea-pig, we need introduce minute doses only of the serum of persons who have recovered from an attack of cholera. Lazarus[737] was the first to make this interesting observation. In three cases of cholera studied by him, the serum withdrawn some time after recovery exhibited an extraordinary protective power: a decimilligramme of the blood serum of these patients was quite sufficient to prevent the death of a guinea-pig inoculated intraperitoneally with the cholera vibrio. Soon after, G. Klemperer[738] made a similar observation in two other cases that had recovered, but the blood, in his convalescents, was much less active than was that in the cases cited by Lazarus.

[Sidenote: [463]]

Issaeff[739], working in Koch’s Institute in Berlin, examined the blood of several persons who had recovered from cholera, and found that the serum had always acquired a specific protective property; this property never developed before the third week from the commencement of the disease, and had completely disappeared as early as three months after this period. Several examples studied by A. Wassermann[740] and Sobernheim[741] fully corroborate this conclusion. Our own researches[742] on twenty-four cases indicate a very great variability in the protective power of the blood of persons who had recovered from cholera. We were able to demonstrate its presence in rather more than 58 per cent. of these cases. Sometimes this power was almost as marked as in the example given by Lazarus, whilst in others it was very feeble, often even nil. We were unable to demonstrate any relation between the gravity of the disease and the strength of the protective power of the blood. Thus, in a moderately severe case of cholera, a very small quantity of serum (0·001 c.c.) was sufficient to protect the guinea-pig from fatal cholera peritonitis, whilst in another, an extraordinarily grave case, even a quantity of 2 c.c. was incapable of producing the same effect. In these two cases the blood had been withdrawn at the corresponding period after the commencement of the disease (seventy-third and seventy-fifth days). Sobernheim (l.c.) found the protective power of the serum most marked in a person who had cholera vibrios in his normal dejecta, but who was always in good health and was only examined because he was living with cholera patients.

[Sidenote: [464]]

All these observations point to the fact that neither recovery from, nor immunity against, cholera can be regarded as a consequence of the protective power of the blood. This power does not manifest itself until some time after complete recovery has taken place, and then disappears too soon, that is to say at a moment when acquired immunity ought still to be maintained. On the other hand, the irregularity in the protective power of the blood indicates that this humoral property is something secondary. Since Asiatic cholera is an intoxication by the cholera toxin, we can readily understand that the protective power, resulting from the invasion of the living parts of the organism by the vibrios, should here play a part of little importance. We know already that this power is due to the presence of substances manufactured by phagocytic elements, placed in contact with vibrios. In the experimental infection of rabbits by the cholera vibrio, as demonstrated by Pfeiffer and Marx, the cells of the spleen, of the lymphatic glands, and of the bone-marrow, produce the protective substances. We have no idea of the source of these substances in Asiatic cholera in man.

Asiatic cholera, being an example of intoxication of intestinal origin, it might be supposed that the antitoxic power of the body fluids should be specially manifested after recovery has taken place. On this point our knowledge is as yet very imperfect, because it was not until after the end of the last epidemic of cholera that we learnt how to prepare the toxin. In a case of cholera (M.S.), contracted in our laboratory, the blood serum was examined to ascertain its protective power and its antitoxic activity. This fluid, withdrawn more than three weeks after the commencement of the disease, was found to be protective only in a large dose (0·5 c.c.), in which dose even the serum of normal persons is capable of producing the same effect. It was found in an experiment with suckling rabbits that the antitoxic property of the blood serum of M.S. was nil. It did not prevent these rabbits from dying of intestinal cholera after the absorption of the vibrios, in spite of a dose of three c.c. of serum injected some time previously.

This experiment, unique up to the present, is, of course, insufficient to enable us to affirm that recovery from Asiatic cholera may take place without the development of antitoxic power in the body fluids. That this is so is, nevertheless, probable. In other intoxications of microbial origin, certain data have been collected which point to the same conclusion. Thus, Knorr[743] observed that the blood of guinea-pigs which had recovered from tetanus did not exhibit any antitetanic power. Vincenzi[744] made a similar observation in a man who had recovered from tetanus.

[Sidenote: [465]]

[Sidenote: [466]]

We are much better informed as to the antitoxic property of the blood of persons who have recovered from diphtheria. Klemensiewicz and Escherich[745] have studied two cases of diphtheria in which the defibrinated blood withdrawn some time after recovery was found to be protective for the guinea-pig against a lethal dose of diphtheria bacilli. This fact has been confirmed by several other observers, especially by Abel[746] and Orlowski[747], the latter of whom made his researches under the direction of Escherich. In these experiments the antitoxic power of the blood was demonstrated against diphtheria toxin employed without bacilli. According to the data collected by the above authors the antitoxic property of the body fluids was not exhibited during the early days of convalescence, but was well marked in the second week after recovery. This power was maintained for a short time only, disappearing in a few months. Amongst the observations collected on this subject the most interesting is that made by Escherich. In an infant examined for the first time whilst it was still in good health, the blood was incapable of protecting the guinea-pig. Some time after this negative result had been obtained the child was attacked by a mild diphtheria, which gave rise to the development of antitoxin, for its blood when again examined exhibited a very high antitoxic power. This proves most clearly that even a slight attack of diphtheria is capable of producing antitoxic power in the body fluids. This observation may be utilised to explain the frequency of the presence of this property in the blood of persons in good health who, according to their own statements, have never had diphtheria. This fact has been established by the researches of A. Wassermann[748], Abel (l.c.), and Orlowski. According to the last observer, the blood in one-half the children in the hospital at Gratz who had not been attacked with diphtheria was antitoxic against the diphtheria toxin, sometimes even to a higher degree than was that of the children who had recovered from this disease. Wassermann has demonstrated that in adults this antidiphtheritic power of the blood is even more frequent than in children, and that it increases with age. Nevertheless, these persons affirm that they have never had an attack of the disease. To explain this very paradoxical fact, Wassermann asked himself whether the individuals whose blood was antidiphtheritic did not owe this property to the action of pseudo-diphtheria bacilli. Although incapable of causing the disease, these bacilli might, perhaps, exert a certain immunising influence and give rise to the production of an antitoxin active against true diphtheria toxin. Researches, directed to the clearing up of this point, have not led Wassermann to reaffirm his suggestion. It must be observed that the varieties of these pseudo-diphtheria bacilli are numerous, and that some of them, perhaps, may be capable of fulfilling the function suggested by Wassermann. On the other hand, it is proved that the specific and virulent diphtheria bacillus may be found in the throat of persons in good health either without inducing diphtheria, or only giving rise to a very slight form of disease of very short duration. We must bear in mind that in persons who have not had typhoid fever, but who live among patients suffering from this disease, the blood may be very agglutinative (Foerster); that in others, unattacked by cholera but containing Koch’s vibrios in the intestine, the blood may acquire a high specific protective power (Sobernheim). It is probable that the same rule applies also to the case of diphtheria, and that, consequently, the blood of persons in good health, but containing the diphtheria bacillus in their bodies, may acquire antitoxic power.

This humoral power, once developed, may even be transmitted from the mother to the foetus and so become hereditary. Abel (l.c.) examined the blood serum of four adult women, taking it from the placenta after parturition. Each time it was found to be distinctly antitoxic against the diphtheria toxin. Later, Fischl and Wunschheim[749], working in Chiari’s laboratory in Prague, studied the blood of new-born children from the same point of view. They showed that in the majority of cases this fluid prevents the production of a fatal disease in the guinea-pig, in spite of the injection of several lethal doses of very virulent diphtheria cultures. The blood of new-born children is equally capable of neutralising the diphtheria toxin, that is to say, of protecting animals against poisoning by this toxin. The above observers do not doubt that this antitoxic power comes directly from the maternal blood through the placental circulation. This fact appears to throw some light on the phenomena of immunity acquired by heredity.

[Sidenote: [467]]

Until quite recently we have had very vague notions as to the possibility of transmitting to descendants the immunity contracted as the result of recovery from an infective disease or after vaccination. It has long been known that natural immunity may be transmitted hereditarily. Certain families or certain races are characterised by a special insusceptibility to certain infective diseases. It must even be admitted that this innate immunity has been transmitted from generation to generation. It is quite otherwise with acquired immunity. We know that as a rule the characters acquired during life are not transmitted to descendants; it is only in special cases, in the very lowest organisms, such as the bacteria and their allies, that we may observe the conservation of certain acquired characters through an infinity of generations. The attenuation of bacteria or the absence of the formation of spores, once acquired under special conditions, may thus be transmitted to their descendants who develop and live under normal conditions.

[Sidenote: [468]]

[Sidenote: [469]]

After the discovery of anthrax vaccine by Pasteur, Chamberland and Roux, and an attempt had been made to vaccinate large flocks of sheep, it was an easy matter to investigate whether immunity acquired by the parents was transmissible to their offspring. Several observers, amongst whom I may specially cite Chauveau[750], Rossignol and Cienkowski, got together a certain number of data bearing on this question. These data showed distinctly that, in certain cases, the lambs born from vaccinated sheep presented, from birth, an undoubted resistance to the anthrax bacillus. This fact, however, was neither constant enough nor sufficiently marked to enable us to count upon the young animals being in a refractory condition, and thus avoid having to submit them to vaccination by the two Pasteur vaccines. This necessity threw into the background the researches on the hereditary transmission of acquired immunity. It was only much later that this question was again taken up on a purely theoretical basis. Ehrlich[751], to whom science is indebted for so many works of the highest importance upon immunity, again took the initiative in exact and minute researches upon the heredity of immunity, acquired as the result of vaccination against toxins. In this relation he studied the immunity of the descendants of animals immunised against phanerogamic toxins, such as ricin, abrin and robin, and later, in collaboration with Hübener[752], that of the offspring of animals vaccinated against tetanus toxin. Ehrlich proved very clearly that the antitoxic immunity acquired by the father is never transmitted to his progeny. This fact alone is quite sufficient to show that it is not a true immunity that is met with in young animals born of mothers who have acquired a refractory condition; true immunity is transmitted by the sexual elements, the spermatozoon and the ovum. Certain observers, Tizzoni[753] and his collaborators Cattani and Centanni, thought they could overthrow the rule established by Ehrlich. They believed that the male rabbit, vaccinated against rabies, was capable of transmitting its immunity to its progeny. Charrin and Gley[754] expressed the same opinion as regards animals of the male sex vaccinated against experimental pyocyanic disease. But the very precise experiments of Wernicke[755], Vaillard[756] and Remlinger[757] upon a whole series of infective diseases and intoxications, such as diphtheria, cholera peritonitis, anthrax, experimental typhoid septicaemia, etc., showed conclusively the correctness of Ehrlich’s results. Well-vaccinated males, even when hypervaccinated, never transmit their immunity to their descendants. This acquired property, like so many others, is not hereditary in the strict sense of the word. The females, on the other hand, with rare exceptions, transmit their acquired immunity to their young, but this transmission can in no way be attributed to the ovum; it is here, then, no longer a question of hereditary immunity properly so called. According to Ehrlich the female furnishes in her blood plasma the antitoxin which passes into the circulation of the foetus. In all respects this is allied to the so-called passive immunity (or antitoxic immunity of von Behring). It is due entirely to the direct introduction of antitoxin, manufactured by the cells of the maternal organism, into the body of the progeny. The living elements of the foetus play no part in it, and it is for this reason that the antitoxins and immunity in the new-born animal disappear so very rapidly,—within a few weeks after birth. Wernicke accepts the views of Ehrlich in their entirety. He found that the immunity of female guinea-pigs was transmitted to the new-born animal; but this hereditary transmission was exhausted in a single generation; it was not found in the second generation. Wernicke was able to demonstrate that the refractory condition in guinea-pigs, born of mothers vaccinated against diphtheria, persisted for three months. Vaillard found that it was retained in certain cases for an even longer period,—up to the fifth month. On one occasion he even observed the transmission of the immunity to a second generation. A female guinea-pig, born of a mother immunised against tetanus, gave birth to a young one which, when tested a month after birth with a ten times lethal dose of the toxin, contracted merely a slight tetanus.

From this fact, as well as from the fact that the immunity of the young ones born of vaccinated mothers persists longer than does that conferred by the injection of antitoxic serum, Vaillard concludes that there exists a kind of hereditary immunity which is “fixed” by the cells. He thinks that not only the antitoxins and other antibodies but also certain living elements, especially the leucocytes, are able to pass from the maternal blood into that of the foetus and to transmit to it the properties acquired by the mother. At this point we may recall the facts demonstrated by von Behring and Ransom that antitoxin persists much longer in the blood of an animal when it is introduced with the serum of the same species. (We have described these observations in Chapter XII.) Now, since in hereditary transmission the antitoxin passes over with the blood plasma of the same species, whilst in the experiments on antitoxic immunity it is generally injected with the serum of a different species, it is easy to understand that the former should persist for a longer period than the latter. It is, therefore, very probable that this immunity of the offspring from vaccinated mothers is not in any way a case of true hereditary immunity, but is due simply, as maintained by Ehrlich, to the passage of ready prepared antibodies from the mother to the foetus. In the immunities against diphtheria and tetanus we have the direct passage of antitoxins; in transmitted immunity against infection by the vibrios of Koch and Gamaleia, so carefully studied by Vaillard, we have, very probably, the passage of corresponding fixatives from the mother to the foetus.

[Sidenote: [470]]

Dzierzgowsky[758] in a recent study on hereditary immunity denies the passage of antibodies and toxins through the placenta. He thinks that the foetus does not acquire its immunity through the blood of the mother, but at a very much earlier period. The ovum contained in the Graafian follicle would, according to this observer, come in contact with a fluid very rich in antitoxin, whence it might imbibe the necessary amount of this antibody to ensure the immunity of the new-born animal. Dzierzgowsky bases this opinion on experiments in which antidiphtheria serum injected into pregnant goats and dogs did not produce any antitoxic power in the blood of the foetus. But in the experiments on these animals the injections consisted of the serum of the horse—a different species. This must modify, profoundly, the conditions of the passage of the antitoxin through the placenta.

Dzierzgowsky made a single experiment upon a mare, immunised with diphtheria toxin, and its foal. Whilst the serum of the former was markedly antitoxic, that of the foal did not possess this property in the slightest degree. Hence the conclusion that the antitoxin of the mother had not passed into the blood of the foetus. But the blood of the foal was not withdrawn until some ten months after birth. Now, as the so-called hereditary immunity only lasts for a very short time Dzierzgowsky’s experiment supplies no evidence against the passage of antitoxin through the placenta.

In order to prove that the immunity against toxins may really be acquired by the ovum, Dzierzgowsky[759] carried out a series of experiments with the eggs of fowls immunised against diphtheria toxin. The yolk of the egg, in accordance with the discovery made by F. Klemperer, contained antitoxin; and this antitoxin passed into the blood of the hatched chickens. These facts, though in themselves very interesting, cannot be used to refute the view that antitoxins pass through the mammalian placenta. It is true that this view is perhaps not yet completely proved, but it accords well with all the known facts. Thus, the frequent presence of diphtheria antitoxin in the blood of new-born infants is explained much better on the assumption that it passes through the placenta than that it is due to an immunisation of the ovum surrounded, in the Graafian follicle, by antitoxic fluid. It is difficult to conceive how this immunity could be so fully retained during the nine months of pregnancy.

[Sidenote: [471]]

In support of his interpretation of the phenomenon of immunity transmitted by the mother to her progeny Ehrlich invokes his beautiful discovery of the immunity conferred by the maternal milk. A vaccinated female is capable of communicating to her young a portion of the antibodies manufactured in her organism, not only by the blood channels, but also, in certain cases, by the milk with which she feeds her young.

[Sidenote: [472]]

The transmission of antitoxins by milk has been demonstrated by Ehrlich, and this has since been confirmed by many observers (see Chapter XII). When Ehrlich found that the immunity of the progeny is retained for a longer time than is that which is conferred by injections of antitoxic serum, he conceived the idea of investigating whether the cause of more prolonged retention did not reside in the transmission of the maternal antitoxin by the milk. With the object of verifying this he took, at the moment when they had given birth to young, unvaccinated mice and mice that had been vaccinated against various toxins (ricin, abrin, tetanotoxin). He so changed the progeny that the vaccinated mothers nourished the young born of the normal mice, whilst the normal mothers suckled the offspring of the vaccinated mice. The result of these ingenious and delicate experiments fully confirmed his anticipations. The vaccinated mice transmitted their immunity not only to the young ones to which they had given birth but also to those they had merely nourished with their milk. This observation proved, to demonstration, that the antitoxins are absorbed by the alimentary canal, a very important fact from several points of view. Later researches have shown that only very young mice are capable of assimilating antitoxin through the intestinal wall. Adult mice, fed by Ehrlich with quantities of antitoxic milk, acquired neither immunity nor any antitoxic property of the blood. Later, Vaillard (l.c.) was able to show that even the young of other species of animals such as the guinea-pig and the rabbit are incapable of appropriating the antitoxins from milk by the alimentary canal. He repeated Ehrlich’s experiments with new-born guinea-pigs and rabbits which he caused to be suckled by mothers vaccinated against tetanus. These young rodents, so treated, were found to possess no immunity whatever; they were not able, therefore, to absorb the antitoxin found in the milk of their nurses. Remlinger (l.c.) made similar experiments with young guinea-pigs and rabbits suckled by foster mothers which had been vaccinated against the coccobacillus of typhoid fever. As in Vaillard’s experiments, the result was negative, the milk of the foster mother did not communicate any refractory condition to the nurselings. Remlinger drew the same conclusion from his researches on the transmission of the agglutinative property of the body fluids. When female rabbits and guinea-pigs are vaccinated during gestation the young ones acquire, along with the immunity against the typhoid coccobacillus, a certain agglutinative power of the blood serum. When, however, these vaccinated females suckle the progeny of non-vaccinated mothers the agglutinative power of the milk of the foster mother never passes into the blood of the nurselings. Some years before this, Widal and Sicard[760] had demonstrated the same fact that young rabbits and new-born kittens, when fed with agglutinative milk, acquired no power of agglutinating the typhoid coccobacillus. They agreed with Ehrlich, however, that the blood serum of young mice fed with agglutinative milk acquired the power of agglutinating the typhoid micro-organism.

[Sidenote: [473]]

As it was important to determine whether the human subject was capable of acquiring a certain immunity by absorbing antibodies contained in the milk, the study of this question was taken up, especially from the point of view of agglutinative power. Although the relations of this agglutinative power with immunity are very problematical it would be interesting, bearing in mind the analogy between the agglutinative, antitoxic, and protective properties, to ascertain whether the ingestion of agglutinative milk can confer any agglutinative property on the blood serum. Numerous researches in this direction were carried out in connection with typhoid fever. Widal and Sicard (l.c.) caused a person to drink daily (for a period of three weeks) half a litre of milk coming from an immunised goat, a milk which powerfully agglutinated the typhoid coccobacillus. The blood, examined on several occasions, never showed the slightest agglutinative power. This experiment goes to prove that, in the adult human subject, the agglutinin does not pass from the alimentary canal into the circulation. May it not perhaps be otherwise in infants which are fed on milk only? An observation by Landouzy and Griffon[761] seemed to confirm this supposition. They first demonstrated the agglutinative power of the blood serum in a woman who had contracted typhoid fever three months after her lying-in. Being a mild attack the woman continued to suckle her child during the whole course of the fever. On examination of the blood of the infant it was found that the serum agglutinated the micro-organism of typhoid fever. These observers did not measure the agglutinative power of the blood, either in the infant or in the mother. This omission deprives their observation of value since it is now recognised that normal human blood fairly frequently exhibits some power of agglutinating the typhoid coccobacillus. For diagnostic purposes it is necessary, therefore, always to measure this power in order to be sure that it is higher than that of the normal blood.

It is all the more difficult to draw any positive conclusion from the observations of Landouzy and Griffon because in several similar cases the result has been entirely different. Thus Achard and Bensaude[762] have shown that the blood of an infant, suckled by a nurse attacked by typhoid fever and whose serum became distinctly agglutinative, was incapable of bringing about clumping of the typhoid coccobacilli. Schumacher[763], working in Fraenkel’s laboratory in Halle, studied a case with very great care. A woman gave birth at full term to an infant whose blood serum exhibited a certain agglutinative power. The mother suckled the infant from its birth. Although her milk manifested a very considerable agglutinative property, the blood of the child exhibited not only no increase in agglutinative power but a marked diminution. The agglutinin of the maternal blood had not passed into the fluids of the child.

[Sidenote: [474]]

From the point of view of the impossibility of acquiring immunity by suckling, therefore, the human subject may be grouped with the guinea-pig, rabbit and cat. Up to the present the mouse is the only exception. It would be very important, with the object of finding a means of communicating immunity by way of the intestine, to study the precise conditions which govern this phenomenon. In hereditary immunity, or rather in what appears to be such, those cases where the new-born animal exhibits a resisting power induced by the vaccination to which it has been subjected in the womb of the mother must be borne in mind. We have already cited the example given by Remlinger of rabbits and guinea-pigs born refractory against the typhoid coccobacillus, which had been injected into the mother animals. In those cases where the vaccination of the mothers has been carried out during the period of gestation the immunity of the young ones is more permanent than when it was completed before that period. Into this same group come those cases where women, vaccinated during the course of pregnancy, give birth to infants refractory to vaccine. Similar facts have been reported by veterinary surgeons with regard to sheep-pox; Arloing, Cornevin, and Thomas[764] have offered similar demonstrations with regard to symptomatic anthrax.

These results may be more or less closely associated with those where the child attacked by an infective disease immunises the mother. Such facts are rare. We know that a healthy mother may give birth to a syphilitic child; the affected father introducing the virus with the sperm, the contaminated foetus contracts the disease and the new-born infant is syphilitic. According to Ehrlich and Hubener (l.c. p. 54), the foetus instead of infecting the mother sets up in her a refractory condition. It must be confessed that as yet we do not understand the mechanism of this immunity; but in any case we have here to do with an example of immunity naturally acquired under very special conditions.

Here again must be recognised another form of immunisation:—where the child born of a syphilitic mother remains healthy and contracts syphilis neither by the breast nor through the kisses of the mother. Here, undoubtedly, we have an immunity against syphilis acquired in the womb of the mother, who may, however, readily communicate her disease to other persons by means which are without effect on her own infant. This example comes under the law of Profetta. Here again the mechanism of the acquired immunity is absolutely unknown.

[Sidenote: [475]]

It must be admitted that, generally, we are still very imperfectly informed concerning immunity as acquired by natural paths. In cases where this immunity is developed as the result of an attack of an infective disease the phenomena observed closely resemble those that have been observed after vaccination by living, fully active, or attenuated viruses, by micro-organisms which have been killed, or by the products of these micro-organisms. These vaccinations which bring about isopathic (von Behring) or active (Ehrlich) immunity give rise to transient and mild diseases and are confined almost completely to the diseases contracted by natural means which terminate in recovery and give rise to a refractory condition. The immunisation of the foetus comes into the same series.

On the other hand, the immunity which was believed to be hereditary and which results merely from the direct passage of the antibodies of the blood or of the milk of the mother to the foetus and to the child come into a group of cases characterised by what Ehrlich has termed a condition of passive immunity. We have already discussed (Chapter X) the thesis that this term “passive” is applicable only in rare cases. Most frequently it is necessary that the living cells of the organism which receives the antibodies—antitoxin, fixatives or others—should contribute their quota in order to ensure the refractory condition. This rule is undoubtedly applicable to the examples of immunity acquired by the new-born progeny of unaffected mothers.

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XV. PROTECTIVE VACCINATIONS

Vaccinations against I. Small-pox.—II. Sheep-pox.—III. Rabies.—IV. Rinderpest.—V. Anthrax.—VI. Symptomatic Anthrax.—VII. Swine Erysipelas.—VIII. Pleuropneumonia in the Bovidae.—IX. Typhoid Fever.—X. Plague.—XI. Tetanus.—XII. Diphtheria.

[Sidenote: [476]]

In the preceding chapters I have attempted to present to the reader a general view of the phenomena of immunity against infective micro-organisms and against their toxic products. I shall now attempt to give a review of the facts acquired in connection with the prevention of the infective diseases of man and of the chief domestic animals by means of vaccination. Vaccinations as we know can be carried out either with viruses the constituents of which have not as yet been recognised, with micro-organisms grown on various nutrient media, with virulent or attenuated micro-organisms, or with microbial products deprived of the micro-organisms by which they have been built up. In addition to these methods we may vaccinate with protective or antitoxic serum and other body fluids, with normal serum, or with a whole series of fluids not excepting water.

[Sidenote: [477]]

I. Vaccination against small-pox.—We naturally commence the series with vaccination against small-pox, which is one of the oldest and one of the best known, having been practised in every country in Europe for more than 100 years. Small-pox, a very contagious and fatal malady, was very rife in the 18th century. Large cities like London and Paris were severely affected. One-tenth of the total mortality was due to this disease. According to statistical information, very exact for that epoch, the deaths from small-pox in London during the course of the second half of the century (1751–1800) numbered more than 100,000 (102,112) persons. During the first half of the same century this disease caused great ravages in France, especially in Paris, where, according to certain statistics (Haeser), about 14,000 persons died in 1716.

[Sidenote: [478]]

Variolisation or “inoculation” coming to Europe from the East, had come into extensive use when, at the end of the 18th century, the discovery was made that cow-pox, the varioliform disease of the Bovidae, produced in persons who milked cows suffering from this eruption an immunity against small-pox. This idea, popular in origin, was known to breeders in England, France, Germany, and Holland; we have thus an indication that this knowledge must date from a fairly distant period. Jenner gave the question a scientific and experimental basis, and it was only after his intervention that vaccination by the contents of the pustules of cow-pox began to spread more generally. During the 19th century an immense amount of material bearing on this question was collected; we have thus been enabled to attain absolutely exact results, and that in spite of the very imperfect state of our knowledge on the etiology of small-pox and of cow-pox. Long ago Chauveau[765] demonstrated that the virus of these diseases must be organised, because that of the vaccine would not pass through a filter. This organism has been carefully sought, but sought in vain in spite of all improvements in microbiological methods. It was thought that the cocci so often found in the contents of the vaccinal pustule was the specific micro-organism of cow-pox. Such was the opinion of the illustrious botanist Cohn[766]. It was soon shown, however, that this was not the case. The cocci, principally staphylococci, are “secondary” micro-organisms which may be absent from the vaccine without its losing anything of its action. A search was then made for the micro-organism of the vaccine among the protozoan organisms. L. Pfeiffer[767] announced the discovery of a species of vaccinal Amoeba. Guarnieri[768] has even described various stages in the reproduction of this hypothetical parasite; but Salmon[769] demonstrated, in a work carried out in the Pasteur Institute, that we had here to deal merely with leucocytes which had entered epithelial cells and had there undergone marked degeneration. Funck[770] thought that he was able to confirm the discovery of the sporozoon of vaccinia, but his error was easily demonstrated (Podwyssozki and Mankowski)[771]. Up to the present, then, we have no knowledge of either the micro-organism of small-pox or of that of vaccinia. We still employ, as formerly, the virus taken from the vaccinal pustule. Even the relations which exist between the two viruses and the two diseases which they have set up have not yet been settled. Several authors believe that the bovine disease is only a modified and attenuated form of human small-pox; whilst others maintain that we have two very different exanthemata, one of which—cow-pox—is capable of setting up immunity not only against itself but also against small-pox.

[Sidenote: [479]]

For a long time, in order to vaccinate against small-pox, the contents of the vaccinal pustules which formed on the human subject after an original inoculation of the virus of cow-pox were employed. But a number of cases of infection by syphilitic virus and certain other accidents caused this method to be abandoned. A number of years ago, however, there spread throughout Europe and into several countries of other continents another method, which consists in vaccination by “animal lymph,” that is to say, by the contents of pustules developed on the skin of the calf. This method was first carried out at Brussels in 1868, under the direction of Warlomont, at the Institute founded by the Belgian Government for the preparation of vaccine. The original virus came from a genuine case of cow-pox and has since been kept up by uninterrupted passage from calf to calf. The virus is introduced into the shaved skin of the region between the groin and the udder as far forward as the umbilicus. It is inoculated superficially into the epidermis by cuts one centimetre long. At the points of inoculation characteristic pustules develop; from these the vaccinal content is withdrawn, on the fifth day in summer or the sixth in winter. The contents are removed by pressure and by scraping the pustules. The scrapings are mixed with water and glycerine. The vaccine thus prepared is put into small glass tubes which are sealed at both ends. This method, with slight modifications, has extended to many other countries, and is carried out either in private establishments or in State institutions as in Germany. For the purpose of purifying the vaccine it is diluted and then allowed to sediment or it may be subjected to centrifugalisation. The object of these measures is to rid the “lymph” of the micro-organisms which accompany it. This object is, however, only imperfectly attained and is moreover accompanied by an attenuation of the vaccinal action. On the other hand, precautions are taken to ensure all possible cleanliness during the operation of inoculation and whilst the calves are under treatment. Thus, great care is taken to disinfect the area of inoculation with alcohol or some other antiseptic and to dress the pustules during the course of their development. Similarly the arms of the patient to be vaccinated are well washed; following in this the rules of asepsis rather than of antisepsis for fear that the vaccinal virus might be destroyed by antiseptic substances. Various instruments are made use of for vaccination and care is taken to sterilise these before they are used. Sometimes the lancet is used, sometimes “plumes à vaccin” or vaccinostyles, or a bistoury of iridio-platinum (Lindenborn) etc.

When the vaccine is of good quality and the operation of vaccination is well done, there is no doubt as to the protective result obtained against small-pox. The observations that have been collected for a great number of years past, in many countries, place this beyond doubt. There are, indeed, statistics from which it is impossible to draw any precise conclusions because they are founded upon too scanty figures or deal with conditions that are too complex. This is the case with the Swiss vaccinations. Certain cantons (such as Zug and Uri) have made vaccination obligatory, whilst others (Bern, Zurich, Lucerne, etc.) some years ago abolished the law which compels the vaccination of all children in infancy. It happened that for some years small-pox had more victims in the cantons of the first group than in those of the second. The opponents of antivariolic vaccination attempted to use this as an argument against the utility of this method. But a more detailed study of the facts clearly shows that it is impossible to draw from it any conclusion whatever. Even in those cantons where vaccination is supposed to be compulsory this law is not carried out rigorously, and the number of persons vaccinated often does not exceed that in the cantons where it is not obligatory.

[Sidenote: [480]]

In order to gain some idea of the utility of vaccinations we must collect statistics on a much larger scale than are those obtainable from the Swiss cantons. Germany furnishes such statistics. Compulsory vaccination was introduced there more than a quarter of a century ago (1874), and statistical information has been collected with great care. With the exception of a slight increase during the period from 1879 to 1885 small-pox has diminished progressively since the proclamation of the new law, and has become so rare that in 1897 there were only 5 fatal cases in the whole German Empire. In the space of 13 years (1886–1898), in a population which embraces two-fifths of the total inhabitants of the German Empire, there were altogether five fatal cases of small-pox occurring in persons who had been successfully revaccinated. Moreover, the majority of the cases of small-pox occurred in the maritime towns or in the vicinity of the frontier of the Russian Empire.

Specially favourable results have been obtained in the German army, in which, even before the law of 1874, vaccination was compulsory. In 25 years there occurred in the Prussian army only two cases of death from small-pox. In summing up the statistical data on vaccination Kübler[772], from whom we have borrowed the above statements, expresses himself as follows: “The history of small-pox must in all cases register the fact that this dreaded disease has, as the result of general vaccination, not only become rare in the German Empire but that it has almost completely disappeared” (p. 365). The example of Germany encouraged several other countries to introduce compulsory vaccination, and Roumania, Hungary, and Italy have in turn promulgated similar laws. Here also it was not long before satisfactory results were obtained. In Italy especially the mortality from small-pox has largely decreased in recent years.

[Sidenote: [481]]

In England, where compulsory vaccination was introduced some time ago, it was abolished in 1898. As the opposition of the people became more manifest, the law, although it continued to exist formally, was carried out very imperfectly. The number of unvaccinated children had gradually increased in such a fashion that in London itself in 1897–1898 it attained the proportion of 24·9%, whilst in certain provincial districts it has oscillated between 78·4 and 86·4%. Under these conditions, the abolition of the law of compulsory vaccination was only the legal sanction of an accomplished fact. According to the details which have been supplied to me by the Jenner Institute in London (which has taken in hand the distribution of vaccine), vaccinations since they are no longer compulsory have become more frequent in England, and the quantity of vaccine distributed has increased considerably. This quantity, however, is not adequate because small-pox has again made its appearance in London in the form of a pretty serious epidemic[773].

In France a law is being framed which will render infant vaccination compulsory. Up to the present this has not been the case, and small-pox from time to time causes considerable ravages, as we may see at this moment in Paris. During recent years the mortality from small-pox in France has been from 90 to 100 times greater than in Germany. It is greater amongst the female population than amongst males; this constitutes a fresh argument in favour of vaccination. Although not compulsory for the whole of the French population, it is so for soldiers and for children who carry on their studies in schools, and it is for this reason that small-pox is rarer amongst males. The most complete demonstration of this is found in the incidence of small-pox in the French army. In spite of a less numerous contingent of troops (451,941–457,677) the mortality from small-pox was greater during the period when vaccination was not yet carried out generally (1885–1887) than during the period (1889–1896) when it was rigorously enforced on a much larger number of soldiers (524,733–564,643). From 13·6 fatal cases per year in the first period the annual figure fell to 6.

[Sidenote: [482]]

It follows, when we take into consideration the whole of the very numerous data at our disposal, that the usefulness of vaccination followed by revaccination after some (5–7) years cannot be seriously called in question. As to the inconveniences that may be caused, they are observed in very rare cases, and then most frequently when impure vaccines are used, or when the vaccinated skin becomes contaminated. According to the German statistics there were registered in the space of 13 years (1885–1897), in 32 millions of vaccinations, 113 fatal cases as the result of infection of the wounds. In forty-six of these it was proved that the small wound had been contaminated by impurities introduced by those attending on them. The remaining 67 fatal cases could be ascribed to the vaccines themselves. We must, however, still regard these cases as too numerous and as being readily avoidable by the adoption of rigorous asepsis. To sum up, the anti-variolous vaccination by the virus of cow-pox constitutes a method of very great value in the prevention of one of the most dreaded of infective diseases, but it is evident that improvement can still be made in this branch of practice. If science should succeed some day, as we may be permitted to hope it will, in finding the micro-organism of vaccinia and of small-pox, and it should succeed in growing it in pure media, it might react very beneficially on the practical application of vaccination. The more simple the methods, the less chance will there be of the occurrence of those unsuccessful cases which, even now, are rare exceptions.

II. Vaccinations against sheep-pox (la clavelée).—Sheep-pox, being a disease very similar to human small-pox and very serious from an economic point of view, the idea was conceived of fighting it by methods similar to those used against small-pox. Since the 18th century there has been practised on a large scale the artificial immunisation of sheep by the inoculation of the virus of the sheep-pox (clavelisation) just as the variolisation of man was practised before the discovery of cow-pox. For this purpose it was necessary to have a considerable quantity of virus; this was obtained by inoculating sheep-pox into the skin of sheep. This inoculation was effected either with a lancet or, according to Soulié’s method[774], by means of a Pravaz syringe. The pustules, developed under these conditions, were generally of large size and capable of furnishing a considerable quantity of the virulent lymph (claveau) used for immunisation. This fluid, when gathered pure, and kept in a closed vessel protected from light and heat, retains its virulence for a long time: unlike what is observed in the case of vaccine, the addition of glycerine destroys the virulence of the lymph pretty quickly. For use, the lymph is diluted with ten times its volume of 2% borated water; the fluid thus obtained is inoculated into the extremity of the tail or of the ear; usually a pustule, which remains single, is formed at the point of inoculation. Clavelisation rarely sets up a generalised eruption which is always serious and sometimes fatal.

[Sidenote: [483]]

In France the law ordains the clavelisation of flocks in which sheep-pox appears; but it interdicts its practice in unattacked flocks;—it is easy to understand the reason for this; in infected flocks all, or almost all, the sheep, gradually become ill and the illness lasts for some time; clavelisation diminishes both the duration and the gravity of the disease; the mortality that it causes, although sometimes very great, the French sheep being very susceptible to sheep-pox, is always much less than that due to a natural contagion;—on the other hand, the clavelisation of a healthy flock, beyond the fact that it may cause considerable losses, is attended by the special danger that it creates centres from which the contagion may invade all the flocks of the district.

But there are countries in which protective and general clavelisation does not present these inconveniences—the countries where the disease is endemic and where the sheep are very resistant to the action of its virus. This is the case in Algeria; sheep-pox exists there permanently without doing much damage; but the Algerian sheep, which take sheep-pox without suffering any apparent illness, communicate to French sheep amongst which they are introduced a very malignant sheep-pox which sometimes kills as many as 50 per cent. of the flock. This explains and justifies the measures recently taken by the Minister of Agriculture, forbidding the importation of Algerian sheep into France unless they have been vaccinated at least a month previously.[775]

In many other countries clavelisation is likewise enacted, being authorised in cases where it may be very useful and interdicted in other cases. In certain countries, e.g. Germany, Holland, and Denmark, clavelisation can be put into force by the Government, which alone has the right to authorise it under certain circumstances.

[Sidenote: [484]]

III. Antirabic vaccinations. Vaccination against rabies has this point in common with those against small-pox and sheep-pox, that it is effected with a virus whose micro-organism is as yet unknown. On the other hand, it is distinguished by its efficacy during the incubation period. When persons are vaccinated during the incubation period of small-pox, or sheep during the same period of sheep-pox, the vaccinations by vaccine and claveau are incapable of arresting the disease and the infections continue to follow their normal course. When, on the other hand, we vaccinate men or animals that have been bitten by mad animals or inoculated with the rabic virus by other means, the antirabic vaccination, with rare exceptions, prevents the development of rabies. This vaccination, taking advantage of the length of the incubation period of rabies, constitutes, therefore, a special type, intermediate between protective vaccination, properly so called, and a therapeutic method of treatment.

It is to Pasteur that science and humanity owe the invention of this method. Aided by his collaborators, especially by Roux, he established in the first place a whole series of important facts on the subject of the rabic virus and of experimental rabies. He then set himself to elaborate a practical method capable of preventing the manifestation of the disease in dogs inoculated with rabic virus and in men bitten by mad animals. He succeeded in solving this problem in 1885.

Pasteur’s antirabic vaccines are prepared from the spinal cords of rabbits that have died of experimental rabies as the result of the inoculation of the virus bearing the name of “fixed virus.” Prepared in the laboratory, this virus presents the characteristic feature that when inoculated under the dura mater of rabbits it sets up in them the first rabic manifestations after an incubation period of six or seven days. The disease soon assumes the typical paralytic form which lasts several days. Whilst the period of incubation presents only very limited variation, the time of death is subject to much greater variation, especially according to the season of the year. Sometimes the rabbits will die on the eighth day after the inoculation of the virus: but death may be delayed one or two days, rarely more.

It is necessary to wait for the natural death of the mad rabbits before the spinal cord is extracted, and not to kill them before this term, for it is only during the final moments of life that the rabic virus is abundant and is distributed uniformly through the whole substance of the organ. After removal from the vertebral canal the cord is suspended in glass vessels containing solid potassium hydrate at the bottom. A whole series of cords so prepared are then kept in a dark chamber heated to 23° C. or thereabouts. The progressive desiccation which the cords undergo under these conditions diminishes their virulence. At the end of several days of this treatment the desiccated cord, instead of producing rabies in 6–7 days in rabbits inoculated under the dura mater by trepanning, induces it after longer periods of incubation. Finally, the cords do not produce even the slightest symptoms of the disease.

[Sidenote: [485]]

The fundamental basis of the Pasteurian method consists in the fact that the desiccated cord, inoculated as an emulsion below the skin of animals, produces in them a complete and permanent immunity against inoculation of the most powerful rabic virus beneath the dura mater. This experiment, frequently repeated on rabbits and dogs, justified Pasteur in 1885 in attempting the first vaccinations of persons bitten by rabid animals, especially dogs. The encouraging results of these early attempts led to the foundation of the Pasteur Institute in Paris, devoted, in part, to antirabic vaccinations. Shortly afterwards, antirabic Institutes were founded in many other European towns, and later in North and South America, in Indo-China, the East Indies, and in Africa. At present there are in France six such Institutes (Paris, Lille, Marseilles, Montpellier, Lyons, Bordeaux), in Russia 9, in Italy 6, etc. The last of these institutions founded in Europe is that of Berlin, where it forms a branch of the Institute for Infective Diseases carried on under the direction of Robert Koch. The foundation of an antirabic institute in Berlin had a very important significance from several points of view. In the first place, it indicates the definite acceptance of the Pasteurian method, a method which has been discussed so long and so keenly. Secondly, it proves that even in a State where there is a highly organised sanitary police, antirabic vaccinations may still be of great service.

Seeing that it was in the Pasteur Institute of Paris that the method of antirabic vaccinations was first elaborated and that it has undergone a very prolonged ordeal, the method there used serves as a model for the practice of almost all other institutes. Although in some of them methods which differ more or less from the original may have been introduced, the fundamental principle upon which they are based remains the same.

[Sidenote: [486]]

According to the Pasteurian method properly so called the vaccinal inoculations are commenced with cords that have been dried for 14 days and have thus lost their virulence. A piece five millimetres long is pounded up with very weak veal broth. Up to 3 c.c. of the emulsion thus prepared is injected below the skin of the flank. The same day a second injection of the same quantity of an emulsion of a cord which has been drying for 13 days is made at the corresponding position on the opposite side. Each day an advance is made by injecting emulsions of cord which are increasingly fresh and the treatment is concluded by the introduction of virulent cords, which have been kept at 23° C. for 3 days only. The ordinary medium treatment lasts for 15 days. On the first 5 days two vaccine injections a day are made. On the last 10 days, when gradually fresher and more virulent cords are employed, only a single injection is made each day. The injections are made with syringes of the Pravaz type and are carried out under conditions of rigorous cleanliness.

If the bites are numerous, or if they are situated on exposed parts, the treatment is prolonged for 18 days and is further distinguished in that the cords of 4 and of 3 days are injected much more frequently.

In especially grave cases, when the bites are on the face and head, the treatment extends over 3 weeks. A more rapid progress is made by making four injections instead of two during the two first days; in this way a greater quantity of the virulent cords is injected than in the first two types of treatment.

The effect of the antirabic vaccinations is usually very good. During the early years of their application the results were fully discussed from all points of view, and no efforts were neglected of seeking out objections of every kind. For the purpose of obtaining rigorously accurate statistics a separate division was made, at the Pasteur Institute, for the cases of persons treated after bites inflicted by dogs whose rabic condition had been demonstrated experimentally (by the injection of an emulsion of the bulb below the dura mater or into the anterior chamber of the eye of the rabbit or guinea-pig). A second and special set of statistics was drawn up of cases where the bites had been inflicted by animals whose rabic condition had been recognised by veterinary examination. Individuals bitten by animals that were simply suspected to suffer from rabies were kept separate.

[Sidenote: [487]]

Thanks to this systematic classification we were able, at the Pasteur Institute of Paris, to establish the fact that the antirabic vaccinations performed on persons bitten by animals that were undoubtedly mad resulted in an extremely low mortality from rabies. Finding it impossible to attack these results, demonstrated with the precision of a laboratory experiment, the adversaries of the Pasteurian method alleged that, quite apart from any vaccination, the percentage of cases of rabies in persons bitten by mad animals is not greater than amongst the vaccinated. A hitch in the application of the new vaccinal method soon demonstrated how entirely unfounded was this objection. At the Bacteriological Institute of Odessa, founded in 1886, that is to say almost immediately after the Paris Institute, the first attempts at vaccination were followed by a mortality from rabies of 5·88 per cent., a figure incomparably higher than that of the Paris Institute. Analysing the probable causes of this want of success it was found that the Russian rabbits, being much smaller than the French ones, furnished far too small an amount of vaccinal matter. This being the case, the introduction of a more intensive treatment was sufficient to cause the mortality to drop suddenly to 0·8 per cent. This fact, added to so many other proofs, finally convinced the most sceptical and brought about a general acceptance of the Pasteurian method.

In course of time the number of cases observed has become very considerable and the experience gained in the manipulation of this method very wide. The improvements made in the details of the vaccinal practice have brought about a progressive diminution in the mortality amongst the persons treated. From 0·94 per cent. in 1886 the mortality (counted from the 16th day after the completion of the vaccinations) fell in 1897 to 0·39 per cent., in 1900 to 0·28 per cent. In the space of 15 years (1886–1900) there have been treated in Paris 24,665 persons, of whom 107 died from rabies, giving an average of 0·43 per cent.[776]. The greatest mortality was registered during the early years of the application of the method, and the rate of the later year’s (1896–1900) oscillated between 0·39 per cent. and 0·20 per cent.

The results obtained in the majority of the other antirabic institutes corroborate those of the Pasteur Institute of Paris. Thus, according to the latest statistics of the St Petersburg Institute[777], the mortality, in 1899, among persons who had completed their vaccinations, was about 0·5 per cent. At Berlin[778] there were treated during the same period 384 persons, of whom 2 died from rabies during treatment, whilst a third succumbed on the 14th day after the close of the vaccinations. Only this latter case ought, according to the principles generally accepted, to be counted as an unsuccessful case, this would give a mortality of 0·26 per cent.

Quite recently, the antirabic treatment has been so reinforced that the treatment terminates with the injection of cords desiccated for two days or even one day only. The results of this intensive treatment have not yet been reported upon.

[Sidenote: [488]]

According to the statistics of the Berlin Institute rabies is far from being so rare in Germany as was, at one time, generally supposed. During the year 1899 its presence was demonstrated, by the experimental method, in 206 dogs coming from various districts. It is in Silesia, Western Prussia, and Posen that rabies in dogs has been observed most frequently.

Antirabic vaccinations have also been performed on herbivorous animals (sheep, goats, cattle, and horses) which are immunised by means of injections of the rabic virus into the veins, according to the method suggested by Nocard and Roux[779], as the result of experiments made by Galtier[780].

[Sidenote: [489]]

IV. Vaccinations against rinderpest. For some time attempts were made to find a means of immunising the Bovidae and other ruminants, susceptible to rinderpest, against this terrible disease, which causes great ravages in regions where it is endemic and greater still in those regions where it only appears in epidemic form. The good results obtained from “clavelisation” suggested the idea of immunising against rinderpest by the inoculation of the rinderpest virus, but all such attempts gave unsatisfactory results, the inoculation setting up a rinderpest as grave, and often as fatal as the natural disease. Only in recent years have we succeeded in elaborating methods of vaccination really capable of coping effectively with rinderpest. Koch[781] went to Cape Colony, where this disease had recently appeared and had caused enormous losses, with the intention of finding a practical method of arresting the scourge. In spite of his technique and incomparable skill he was as unsuccessful in finding the parasite of rinderpest as had been other investigators. The micro-organism of this disease remains unknown. It was necessary, however, to seek a remedy against it. Koch, studying the properties of the bile of animals that had died from rinderpest, recognised that the injection of this bile into normal animals conferred upon them a fairly certain immunity, and this fact served as the basis on which to work out a practical method of combating rinderpest on a large scale. At first this method was received with much enthusiasm, but experience soon demonstrated the inconveniences it often presented. Kolle and Turner[782], who continued the researches on rinderpest in Cape Colony, extolled Koch’s method at the commencement of the epidemic with the object of establishing around the original disease centre an unaffected zone which would interfere with the propagation of the disease. They recognised, however, that this method could not be employed generally, for the reason that it does not set up immunity until the end of eight days, during which period the animals may contract the disease. Further, it demands the sacrifice of a large number of animals in order to provide the vaccinal bile required for the vaccinations; finally, it confers an immunity of short duration only (four to six months).

[Sidenote: [490]]

It was necessary, therefore, to find some method that was more generally applicable. With this object Koch himself began to study the blood serum of animals that had recovered spontaneously from rinderpest. He was able to assure not only himself, but several other observers, that this serum was capable of rendering normal animals into which it is injected refractory. Bordet and Danysz, who studied rinderpest in the Transvaal in 1897, made many experiments in this direction and devised a method which gave good results in practice. But it was left to Kolle and Turner to work out a method at once simple and easily applied, one which soon came into general use. This method is known by the name of “simultaneous vaccinations.” It consists in the injection of a protective serum simultaneously with the virulent blood. To prepare the former the authors just mentioned made use of animals that had recovered spontaneously from rinderpest or of Bovidae that had been immunised by bile or by some other method. It was recognised that the protective power of the serum of animals that have recovered is very small and cannot confer immunity on normal animals, except when injected in large doses. Kolle and Turner showed that if Bovidae that have recovered spontaneously are injected with very large quantities of virulent blood coming from animals fatally attacked, the protective power of the serum of the former is markedly increased and a serum is obtained which is active in small doses and which gives good results in practice. This serum may be kept for a long time by the addition of a small quantity of carbolic acid. The immunity conferred by this serum upon normal animals is immediate, but of short duration; it is completed by making a simultaneous injection of virulent blood; we thus obtain a double immunity, one part immediate, the other permanent; to get this result, however, the serum must not be mixed with the virulent blood, for when this is done the immunity conferred is trifling or nil. On the other hand, it is complete and persists for several months when the protective serum is injected separately on one side of the body and the virulent blood on the other.

Kolle and Turner had to defend their method against many ill-founded objections and attacks, but they succeeded in getting it accepted, not only in Cape Colony but also in many other parts of Africa, and in many countries in Europe and in Asia. In 1898 it was decided at a conference which met in Cape Town to use the method of simultaneous vaccinations to the exclusion of all others. This method has since been applied on a very large scale and it was not long before favourable results were obtained. The same method has proved to be very successful with Nicolle and Adil Bey[783] of Constantinople, who now prepare large quantities of the antirinderpest serum, and combat this disease with great success in the Ottoman empire. Yersin[784] adopted the same method to fight the cattle plague in Indo-China, where it causes great ravages, especially among buffaloes. His Institute at Nha-Trang has become a centre for the preparation of the specific serum, which he distributes over a vast territory. In the East Indies the simultaneous method has been applied by Rogers[785]. In Russia, where rinderpest is endemic in many regions, the Institute of Experimental Medicine at St Petersburg furnishes the serum destined to prevent the propagation of this epizootic disease[786].

In a few years this method of simultaneous vaccination has been extended to all the countries ravaged by rinderpest and has already rendered immense services to agriculture.

[Sidenote: [491]]

V. Anti-anthrax vaccinations. In the first four sections of this Chapter we have brought together the methods which have as their basis the vaccination by viruses whose nature is as yet unknown. Since we cannot obtain them by artificial culture, we have to introduce them with animal fluids:—either the contents of vaccinal or clavelar pustules, or matter from rabic nervous centres, or again the blood of animals attacked by rinderpest. In the case last mentioned, in order to prevent the too serious effect of the injection of the virus, it is combined with a simultaneous injection of protective serum.

[Sidenote: [492]]

In the case of the vaccinations against anthrax we pass to the group of viruses whose organised nature is well known and which can be injected in pure culture grown on artificially prepared media. This method constitutes one of Pasteur’s most brilliant discoveries, made in collaboration with Chamberland and Roux. Before they had found a satisfactory method of vaccinating against anthrax these observers had to solve the problem in connection with a less complicated and less difficult case. From the first, in his studies on pathogenic micro-organisms, Pasteur had devoted his attention to finding a means of communicating immunity against these parasites. With the aid of Chamberland and Roux he was not long in discovering a method by which it was possible to attenuate the virulence of the micro-organism of fowl cholera and to vaccinate fowls against this terrible disease by inoculating them with this attenuated micro-organism. Guided by these results Pasteur, Chamberland and Roux set to work to find the vaccine against anthrax; they were soon confronted by a serious obstacle in the formation of spores which prevented the attenuation of the bacilli. This obstacle they overcame by submitting cultures of the bacillus to a temperature of 42°·5 C. Under this condition spores do not develop, and the bacilli become attenuated at the end of a longer or shorter period. Although in possession of these attenuated viruses, it still needed very laborious investigations to adapt them to the vaccination of various species of animals susceptible to anthrax, especially sheep. In this they were also successful, and in 1881, over 20 years ago, Pasteur and his collaborators demonstrated the efficacy of their method on a large number of animals. This demonstration was made at Pouilly-le-Fort before a large commission. We may affirm that this celebrated experiment opened a new path to science and to the practice of vaccination. It was performed on 50 sheep, half of which were vaccinated twice with twelve days’ interval, the other 25 sheep serving as control animals. Fourteen days after the vaccination by the second vaccine all the 50 sheep were subjected to a test inoculation of a very strong anthrax virus. Two days later the vaccinated animals remained unaffected, whilst the control animals had all succumbed to anthrax.

Similar experiments, undertaken in France, Hungary, Germany, Russia and elsewhere, confirmed the efficacy of anthrax vaccinations and led to their extension into all the countries where bacterial anthrax was rife. From the year 1881 the method came into regular use, and before the end of that year there had been vaccinated, in France alone, 62,000 sheep and 6,000 Bovidae. Since these first attempts, made on a large scale, gave such good results, the anti-anthrax practice was not long in spreading through France, then into Hungary and several other European countries. Later, it extended into other continents, especially into South America (Argentina)[787] and Australia. Vaccinations against anthrax were also applied to horses with the same good results[788].

In France the anti-anthrax vaccines are prepared at and sent out from the Pasteur Institute of Paris. These vaccines consist of broth cultures of attenuated bacilli, of which the weakest, the first vaccine, is fatal to the mouse and small guinea-pigs. The bacilli of the second vaccine are less attenuated, and are capable of killing not only adult guinea-pigs but even a certain number of rabbits, when inoculated subcutaneously. The two vaccines are races of the anthrax bacillus, capable of producing spores which present the same degree of virulence as the filamentous bacilli which gave them birth.

The anti-anthrax vaccines are sent out in tubes containing the quantity necessary for the vaccination of a large number of animals. The vaccinations are made especially in spring in order that the animals may be protected during the hot season, which is usually more favourable to the development of anthrax epidemics.

[Sidenote: [493]]

In the sheep the vaccines are injected below the skin on the inner aspect of the thigh. One-eighth of a c.c. of the first vaccine is injected with a somewhat modified Pravaz syringe. Twelve or fifteen days later a similar injection is made on the opposite side with the second vaccine. In the Bovidae the vaccines are injected behind the shoulders, where the skin is thinnest. In the horse the injections must be made on the sides of the neck and shoulders. In large mammals double the amount (¼th of a c.c.) of each vaccine is injected.

The tubes of vaccine, once opened, should not be employed a second time. Care must be taken to use the whole of their contents at one series of vaccinations.

The vaccinal injections produce tumefaction at the point of inoculation and are followed by a slight rise of temperature. But these symptoms are of little importance and soon disappear. Serious complications and fatal results from the vaccinations are very rare. The loss due to these accidents is estimated at one-half per cent. in sheep and a quarter per cent. in the Bovidae.

The refractory condition resulting from the vaccination requires for its development a period of about a fortnight. The immunity is then very substantial and lasts for a fairly long time. According to Chamberland 60% of the sheep retain their immunity a year after they have been vaccinated. But as a great number of animals then become susceptible, it is usual to revaccinate annually.

According to the statistics furnished by the vaccine department of the Pasteur Institute there have been vaccinated, up to the 1st of January 1900, a total of 4,971,494 sheep, and 708,980 cattle. Abroad the corresponding figures are 3,831,948 and 1,869,445. Altogether, the number of animals vaccinated amounted to 11,381,867, of which 3,626,206 have been treated with the vaccine furnished by the Budapest Laboratory.

The results of the anti-anthrax vaccinations were found to be so favourable that it was unnecessary to introduce any improvements in technique. Attempts have certainly been made to prepare anti-anthrax serums, and these have been successful, but up to the present such serums have not been introduced into practice.

[Sidenote: [494]]

VI. Vaccinations against symptomatic anthrax. Symptomatic anthrax, which is often confounded with true anthrax, is set up, as demonstrated by Arloing, Cornevin, and Thomas, by a specific anaerobic micro-organism to which has been given the name of Bacillus chauvaei. Immediately after the discovery of the attenuation of viruses and of vaccines against fowl cholera, the three observers above mentioned tried to apply it to symptomatic anthrax. Finally they devised a method which was soon adopted in practice, and which, for nearly twenty years, has been used in the vaccination of the Bovidae in countries where symptomatic anthrax is most prevalent. This is especially the case in mountainous districts, such as Switzerland, the Bavarian Alps, the Dauphiné, L’Auvergne, etc.

Arloing, Cornevin, and Thomas[789] prepare two vaccines against symptomatic anthrax by a method very different from that used in the preparation of the Pasteurian anti-anthrax vaccines. They take the virus from the muscles invaded by the micro-organism; they triturate a piece of the tumefied muscle in a mortar, adding to it a few drops of water. The mixture is filtered through muslin and the fluid dried at 37° C.; a virulent brown powder is thus obtained. In the preparation of the vaccines a portion of this powder is mixed with water and subjected to a temperature of 100°–104° C. for seven hours. Another portion is heated during the same number of hours to 90°–94° C. only. This latter forms the second vaccine whilst the first portion constitutes the first.

In practice the two vaccinal powders are dissolved in cooled boiled water and are introduced into the subcutaneous tissue of the animals that it is wished to immunise. The second vaccine should be injected 8 to 12 days after the first. The vaccines are usually tolerated very well by the Bovidae and confer upon them a definite and permanent immunity. In spite of certain drawbacks this method, known as the “Lyons method,” has proved to be a very serviceable one and is retained as the best devised up to the present. Its efficacy is proved by the fact that in the period from 1884 to 1895 in 400,000 vaccinated animals the mortality has only been 1 per 1,000. Arloing, Cornevin, and Thomas thought that raising the virus to a high temperature brought about a real attenuation.

[Sidenote: [495]]

Leclainche and Vallée[790], who have recently returned to the study of this question, have shown that this view cannot be maintained. In reality the spores, after being heated to 90°–104° C., gave rise to bacilli endowed with their normal and complete virulence. But the heating in the preparation of the Lyons vaccines destroys the toxin manufactured by the Bacillus chauvaei, with the result, that the spores now become the prey of phagocytes: it is for this reason and for this reason alone that the inoculation of these vaccines is so well tolerated. All the spores of the vaccinal powder are not eaten by the phagocytes: those which are found in the centre of solid particles of the powder offer a prolonged resistance to the action of the cells, and some of them germinating produce bacilli and give rise to a mild disease capable of conferring immunity. The germination of these spores is further facilitated by the presence of foreign micro-organisms in the vaccinal powders; these organisms help to interfere with the phagocytosis of the spores of symptomatic anthrax.

In the course of their researches, Leclainche and Vallée demonstrated that it is easy to vaccinate animals susceptible to anthrax and to confer on them a substantial immunity by means of a single protective injection of a pure culture of Bacillus chauvaei. For this purpose they use cultures grown in broth made from the pig’s stomach (“bouillon de panse” or Martin’s broth) which they heat for 2 hours at 70° C. The cultures, so treated and injected in quantities of 1 to 2 c.c. into Bovidae, induce in them an immediate immunity. These authors are persuaded that the vaccination by this method might be used on a large scale with certain advantages over the method at present in use. A single injection, instead of two, involves a great economy, and the injection of pure vaccinal cultures obviates the accidents caused by the foreign organisms which are found mixed with the Lyons vaccine.

On the other hand, Leclainche and Vallée think that vaccination by serums has no future in the fight against symptomatic anthrax and should only be used in exceptional cases.

It is evident that the Lyons method is capable of being improved and some day may be replaced by another. Still it must be remembered that it has already preserved a very great number of animals from certain death by symptomatic anthrax.

[Sidenote: [496]]

VII. Vaccinations against swine erysipelas. Swine erysipelas is a disease widely distributed in nearly all countries where the breeding of pigs is carried on on a large scale. It is a very fatal disease, and it is estimated that in France alone at least 100,000 pigs of the value of more than five million francs succumb to it annually. Unfortunately swine erysipelas is often confounded by breeders with other epizootic diseases, especially pneumo-enteritis of the pig. This confusion has often resulted in large losses to agriculture.

Soon after the vaccinations against anthrax became a part of veterinary practice, Pasteur[791], assisted by Thuillier, took up the study of swine erysipelas which was causing great ravages in the department of Vaucluse. They were not long in discovering that the true cause of the disease was a very small bacillus capable of growing in pure culture in nutrient broth. Guided by his former investigations, Pasteur with his collaborator undertook minute researches into the reinforcement and attenuation of the virulence of the bacillus of swine erysipelas which led them to the elaboration of a method of vaccination capable of conferring on pigs a high degree of protection against the disease. Following the line of the anthrax vaccinations, Pasteur and Thuillier prepared two vaccines against the erysipelas, the first more attenuated than the second. The bacilli of these two vaccines were cultivated in broth and sent out in tubes similar to those employed in the distribution of the anthrax vaccines.

The vaccines are in themselves innocuous and are capable of communicating to the inoculated pig an immunity sufficiently durable to be of real service. Young pigs being less susceptible to the erysipelas than are the adults, it is generally preferred to vaccinate young pigs of from two to four months. The vaccination is done at two separate times. The first vaccine, in a dose of one-eighth of a cubic centimetre, is inoculated subcutaneously on the inner aspect of the right thigh; the second vaccine is inoculated in the same way, 12 or 15 days later, into the left thigh. The immunity that follows these vaccinations is not fully established until the end of the second week.

[Sidenote: [497]]

In spite of the many advantages of the Pasteurian method the vaccinations against swine erysipelas have not spread so much as one might have expected; and they have found a general application abroad rather than in France. It is only necessary to cast a glance at the statistics to be convinced of this. From the date of the introduction of the Pasteurian vaccinations in 1884 up to the 1st January, 1900, there had been vaccinated in France in all 428,746 pigs, whilst abroad, where the vaccinations were introduced some years later, the number of pigs vaccinated was 4,819,387. Of this number the great majority (4,194,191) had been treated in Hungary. The losses amongst the vaccinated animals were insignificant (1·68%) when compared with an average mortality of 20% amongst unvaccinated pigs.

This limited extension of the vaccination of pigs in France arises from various causes. In many countries the breeding is on too small a scale to allow of the intervention of the veterinarian and of the expenses which the vaccinations involve. On the other hand, it cannot be denied that the Pasteurian method presents certain drawbacks in practice. The living, although attenuated, bacilli introduced may sometimes serve as centres of infection, especially in cases, rare no doubt, where the vaccinated animal contracts a chronic form of the disease. The Pasteurian vaccines must, therefore, be avoided in districts where the erysipelas has not yet appeared. Their application in countries already infected presents the further drawback that the immunity requires for its establishment a fairly long time, sufficiently long to permit the micro-organism to kill a large number of pigs before the vaccines have conferred any immunity upon them.

[Sidenote: [498]]

It is natural that, under such conditions, an attempt has been made to replace the Pasteurian method by some other method less risky. Hence, since the discovery of the principle of sero-therapy several investigators have sought to apply it to swine erysipelas. Emmerich and Mastbaum[792] were the first to demonstrate that the blood of rabbits, immunised with the bacilli of this disease, acquire a very marked protective power. They have even attempted to construct from the results of their researches methods which might be applied practically. It is especially however to Lorenz[793], a Darmstadt veterinarian, that we owe the first practical application of this method. He prepared protective serums by injecting erysipelas bacilli into rabbits and pigs, and demonstrated that the inoculation of these serums, when combined with that of the living bacilli, conferred upon pigs a sufficient immunity and one that was set up immediately after the introduction of the serum. According to Lorenz’s method it is first necessary to give a protective injection of serum; some days (3–5) afterwards this is followed by an inoculation of living bacilli coming from the attenuated erysipelas known in Germany under the name of “Backsteinblattern.” About two weeks later a further injection of the same bacilli, but in double quantity, is given. This method, therefore, involves three vaccinal injections as against two in the Pasteurian method. It is consequently dearer than the latter, but, as it presents certain undeniable advantages, an attempt was made to introduce it into veterinary practice. But being much more complicated endeavours were made to simplify it. Voges and Schütz, by methods which have remained secret, soon obtained a more active serum, and finally Leclainche[794] of Toulouse, after demonstrating that the horse is the best animal for the production of a very active serum, succeeded in devising a method of vaccination as simple as it was effective. He gave to it the name of “serum-vaccinations.” The first inoculation is made with a mixture of specific serum and a culture of living and virulent bacilli. This inoculation is well borne by all pigs and may be made without any regard to the age of the animal. The immunity is set up immediately after the injection of the mixture, but it is not sufficiently durable for the requirements of practice. For this reason Leclainche followed up the first injection by a second, which is made ten to twelve days later and consists of an inoculation of half a cubic centimetre of pure virus. This new method had the special advantage of arresting, almost immediately, the mortality in an infected piggery and of eliminating the chronic cases that are sometimes observed after the Pasteurian vaccinations.

Leclainche[795] has already applied his method of serum-vaccinations to more than five million pigs of all ages. “It has been found to be constant in its effect and absolutely innocuous,” and “not a single case of erysipelas has been met with in pigs that had received the two vaccines,” and Leclainche hopes that his method will soon come into general practice, and that it will be utilised in all cases where the Pasteurian method is found to be insufficient.

[Sidenote: [499]]

As the basis of all the new methods for vaccinating pigs against erysipelas is the preparation of serums capable of preventing the pathogenic effect of the bacilli, the question of the determination of the protective power of these serums comes to be one of considerable importance. At first one was satisfied with certain approximate estimations, but later the necessity was felt of having a more exact measurement. Leclainche is persuaded that of all the laboratory animals capable of being used for these experiments the pigeon is the only one that can usefully fulfil this rôle; very susceptible to the passage virus, it is killed by the bacillus after a regular incubation and invasion period, and the chronic form of the erysipelas, so troublesome in the rabbit and even in the pig, is met with in the pigeon in very exceptional cases only. Leclainche commenced his experiments by inoculating into the pectoral muscles of the pigeon mixtures of serum and virulent cultures. The pigeon received 1 c.c. of a culture of a passage virus mixed with variable quantities of serum. The serum is ready for use in the vaccination of pigs when the pigeons resist the injection of a mixture of ½ a c.c. of serum with 1 c.c. of a virus which kills the control pigeons in 60 to 72 hours.

At the Frankfort Institute of Experimental Therapeutics another method of testing devised by Marx[796] is used. In it injections, below the skin of a series of grey mice, are made of progressively increasing doses of the serum the strength of which it is desired to determine. Twenty-four hours later a virulent culture of the bacillus of swine erysipelas is introduced into the peritoneal cavity of the same mice. The virus is so chosen that the control mice die in about 72 hours. Marx finds that this method gives results which are much more constant and exact than any other; this opinion is confirmed at Höchst, the largest factory of serums in Germany.

VIII. Vaccinations against bovine pleuropneumonia. This infective disease is one of the most dreaded scourges of bovine animals. Very contagious, it has spread from central Europe not only into all the other countries of the European continent, but into Africa, America, and almost every quarter of the globe. The virus of this disease was discovered in the serous exudation of hepatised lungs long before the microbiological period of the Medical Sciences had begun.

[Sidenote: [500]]

Dr Willems of Harselt, who made an experimental investigation, remarkable for the time at which it was carried out (more than half a century ago), demonstrated at once the great virulence of the pulmonary serous fluid; he found also that the effects of the inoculation of the virus varied much according to the seat of inoculation. When made into the trunk, the neck, or the shoulders, the inoculations are usually fatal; at the periphery, the lower part of the limbs, at the extremity of the ears or of the tail, the inoculation ordinarily produces merely an inflammatory tumefaction of small extent, which is absorbed in a few weeks; after this the animal is refractory to the natural disease. Willems concluded from this that we may vaccinate against pleuropneumonia by inoculating the virulent serous fluid of the lung into the tail. Willems’ method of inoculation became a part of current practice 50 years ago.

For the carrying out of a large number of vaccinations it is necessary to have at one’s disposal an adequate quantity of virus; it was therefore to meet this requirement that researches were first carried out. The serous fluid was withdrawn from the hepatised lungs of animals that had succumbed to the disease and was inoculated into normal Bovidae as soon as possible, so as to avoid contamination of the fluid. In fact this pulmonary serous fluid often contains foreign germs capable of multiplying rapidly so that it putrefies very quickly. Pasteur showed that it was possible to remedy these drawbacks by a very simple method by which he could obtain a large quantity of rigorously pure virus. All that is necessary is to inoculate a little of the pleuropneumonic virus below the skin of a weaned calf, behind the shoulder. At the seat of inoculation there is an abundant exudation of virulent serous fluid into the cellular tissue, from which we are enabled to collect large quantities of pure virus.

In some countries, as in Germany and in Australia, institutions have been founded for the production by this method of the virulent serous fluid necessary for these inoculations.

The virus should be inoculated into the tip of the tail of animals that it is desired to immunise, because the temperature in this situation is relatively low and the connective tissue is dense and not very abundant. The inoculation is made with a lancet or a Pravaz syringe. The vaccination is generally borne well, in spite of the reaction phenomena which are manifested about two weeks after the introduction of the virus. At that time a febrile condition is set up and a swelling manifests itself at the point of inoculation, which, however, soon retrogresses and then disappears.

[Sidenote: [501]]

The immunity conferred by Willems’ method is substantial and lasting (for one or two years and even longer); this explains its great success in the hands of breeders and veterinarians. Accidents following its use are rare, and the mortality does not exceed 1 per cent.

In spite of all these advantages a new method was still desirable, a method which would allow of the preparation of large quantities of virus of a suitable and uniform activity under conditions of irreproachable purity. Thanks to the discovery of the micro-organism of pleuropneumonia which we owe to Nocard and Roux[797] this object has been achieved. With the collaboration of Borrel, Salimbeni, and Dujardin-Beaumetz, they succeeded in demonstrating and isolating this micro-organism, the smallest of all known living organisms. The first steps in these researches were very laborious, but later the organism of pleuropneumonia was cultivated on fluid and solid media: Martin’s broth (prepared with pigs’ stomachs) or agar with the addition of a certain quantity (about 5%) of fresh ox serum. The serum-broth, sown with pure pneumonic serous fluid, gives only a moderate growth, which becomes only slightly turbid and contains micro-organisms so small that it is impossible to distinguish them individually. They can be made out only when massed together in irregular clumps. The minuteness of this micro-organism is evidenced by the ease with which it passes through a Berkefeld filter, and even through certain Chamberland candles (F). This feature enables us to obtain the pure virus easily, a fact very important in connection with the isolation of the micro-organism.

[Sidenote: [502]]

Once in possession of pure cultures of the micro-organism of pleuropneumonia, Nocard and Roux attempted to make use of it in practical vaccination. They showed that the organism separated by them is capable of producing typical pleuropneumonia when it is inoculated into the appropriate regions of the body of bovine animals. But when inoculated subcutaneously or into the skin of the tail, it produces merely a mild and transient disease which confers an immunity quite as effectual as that set up by the inoculation of the virulent serous fluid. It may be readily understood that, under these conditions, pure cultures may be much more serviceably employed in the practice of vaccination than can Willems’ virus from the fact that it is easy to obtain large quantities of absolutely pure cultures. It is easy to predict that the new method will soon replace the old one, very great as are the services the latter has rendered to agriculture. Up to the present, vaccinations with pure cultures have been made in several districts in France with very favourable results. The Pasteur Institute and the Veterinary School at Alfort have already distributed to veterinary surgeons more than 5,000 vaccinal doses of culture; the protective action of these inoculations has been at least equal to that of the inoculations by Willems’ method and the resulting accidents have been reduced in the proportion of 20 to 1[798].

The serum of animals hyperimmunised against pleuropneumonia possesses a very distinct protective action, but too little marked and of too short duration to be of any use in practice; it has also a curative action arresting the invading march of a pleuropneumonic congestion; but here it is necessary to intervene early, before the appearance of fever, and to inject large quantities of serum.

The inoculation of a mixture of virus and serum produces no congestion; but it does not confer any immunity; the animal remains just as susceptible as the control to the inoculation of the pure virus.

[Sidenote: [503]]

IX. Vaccinations against typhoid fever. In the preceding sections I have treated more especially of the vaccination of domestic animals against several infective diseases. The information collected on this subject is marked by its great exactness, as it is easy to apply to animals the most rigorous experimental method. In the case of the human subject this is not such an easy matter. As it is impossible to submit him to experimental proof we are obliged to be satisfied with observation, controlled by statistical data. The experience of more than 100 years has, however, been sufficient to demonstrate the great utility of vaccinations against small-pox with the virus of cow-pox which is innocuous for the human subject. In the case of antirabic vaccinations we have to deal with injections into the human subject, first of weakened viruses and then of virulent viruses. Here, however, it is a question of the preservation of the already infected human organism, which, very often, only comes under treatment during the incubation stage of rabies. One can readily understand the hesitation to inoculate even weakened viruses into the human subject, especially when we are not dealing with altogether exceptional cases such as we have in the protection against rabies. We have, therefore, but few examples in which the methods of vaccination by micro-organisms have been applied to man. Such injections were first tried by Ferran[799] against Asiatic cholera. Having succeeded in vaccinating guinea-pigs against experimental cholera septicaemia, the Spanish investigator attempted to inoculate cholera vibrios into the subcutaneous tissue of man, hoping thus to vaccinate him against true cholera. In this way he was able to demonstrate that the subcutaneous injection of living vibrios never sets up symptoms of cholera. The injection is followed by a general reaction in the form of fever, pains in the back and inflammation at the point of inoculation, in a word, transient phenomena of little gravity. Encouraged by these initial results Ferran, profiting by the outbreak of cholera in the province of Valentia, injected into more than 20,000 persons living cultures of Koch’s vibrio. The results published by him did not, however, furnish any real proof of the possibility of conferring immunity against intestinal cholera by means of subcutaneous injections. Later Haffkine[800] modified Ferran’s primitive method somewhat, and instead of living vibrios he injected vibrionic cultures killed by heat or by antiseptics. During the cholera epidemic of 1892 and 1893 he tried the inoculation of these killed vibrios into man, with the object of vaccinating against Asiatic cholera. Later he went to Calcutta in order to try his method on a large scale. He was there enabled to inoculate a great number of persons, and the statistics which he collected appeared to him to be favourable.

[Sidenote: [504]]

But studies on the pathogenesis of Asiatic cholera shook the foundations of Ferran’s method. The injections of vibrios, living or killed, were found quite capable of vaccinating animals against vibrionic peritonitis and septicaemia, but they appear to exert no influence whatever against poisoning by the cholera toxin. When it had been learnt how to set up true intestinal cholera in young rabbits Ferran’s and other similar methods of vaccination were used in vain to prevent the incidence of this disease, which is very similar to Asiatic cholera of man. An experiment[801] made at the Pasteur Institute in Paris upon two persons vaccinated by Haffkine, showed that they were not protected against the choleriform diarrhoea set up by the ingestion of the cholera vibrios. A third person, who had never been “vaccinated” and who served as “control,” after the ingestion of the same cholera culture, behaved exactly as did the other two.

From all these data the conclusion was drawn that in order to prevent intestinal cholera it is necessary to use not cultures of vibrios, living or dead, but antitoxic serums. In fact, the majority of young rabbits vaccinated with these serums and afterwards submitted to infection by the cholera virus through the mouth were found to be vaccinated against intestinal cholera. It has not been possible, as yet, to apply this method to man, hence we are unable to give a decided opinion. Moreover, as the methods based on Ferran’s principle have now been abandoned I have not deemed it necessary to devote a special section to anticholera vaccinations. I could not, however, pass it by in silence, since the attempts to vaccinate man against cholera have led to the trial of a similar method against typhoid fever.

Pfeiffer and Kolle[802] were the first to inoculate man with typhoid coccobacilli sterilised by heat. They observed that these injections caused fever, pretty violent pains in the back accompanied by vertigo, shivering and pain at the point of inoculation, without, however, being in any way serious to health. At the same time they found that the blood serum of inoculated persons acquired a very marked protective power (for guinea-pigs injected into the peritoneal cavity with lethal doses of typhoid cultures) quite comparable to the properties discovered by them in the serum of persons who had recovered from typhoid fever. Pfeiffer and Kolle believed that they thus had a proof of the refractory condition of the individuals whom they had submitted to these injections.

[Sidenote: [505]]

These experiments were continued by Wright, Professor of Pathology at Netley, and it is owing to his unwearied efforts that science finds herself in possession of very important evidence on the subject of protective inoculations against typhoid fever in man. According to a verbal communication made to me by Wright, he has up to the present distributed more than 300,000 doses of his antityphoid vaccine. This vaccine he prepared in the following way[803]. The typhoid coccobacillus is sown in carefully neutralised broth containing 1% of peptone. The flasks of culture are kept in the incubator at about 37° C. for two or three weeks, after which their contents are transferred to large flasks in order to be submitted to a temperature of 60° C. This temperature is quite sufficient to kill all the coccobacilli, but for greater surety Wright added to his cultures one-tenth of their volume of a 5% solution of carbolic acid or of lysol. The vaccine, thus prepared, is examined as to its toxicity for the guinea-pig by means of subcutaneous injections. Wright injects into man a dose of vaccine which is sufficient to kill 100 grammes of guinea-pig (of the weight of 250 to 300 grammes). This dose often amounts to half a cubic centimetre, but it may have to be increased to 1 c.c. and even 1·5 c.c.

The inoculations are made below the skin of the flank or in the shoulder. They are followed by a rise of temperature which commences as early as two or three hours after the injection. This fever is accompanied by pains in the back, nausea, and want of appetite. There may even be collapse; this led Wright to keep his patient in bed for some time after the vaccinal injection. Besides this reaction, there occurs, at the seat of inoculation, a swelling and redness, accompanied by pain; as a rule all these symptoms have disappeared by the end of 48 hours.

[Sidenote: [506]]

Wright convinced himself that the blood serum of individuals treated by his vaccine, at the end of a certain time acquires the property of agglutinating typhoid coccobacilli in a variable, but usually very marked degree. He even thought that this property might up to a certain point serve as the measure of the immunity acquired against typhoid fever. His own researches, however, showed him that this supposition could not be maintained, and that the agglutinative power, varying greatly in strength, might sometimes be absent where the immunity could not be denied. On the other hand, he clearly showed, especially by the experiments with serum collected at the period which precedes the relapses, that the agglutinative property might be highly developed, in spite of the absence of immunity. Wright then set himself to study the bactericidal property of the serum of individuals who had been injected with his vaccine. He devised a very ingenious method of gaining with a minimum loss of time some idea of the fluctuations of this power of the body fluids to kill the typhoid coccobacillus. In the first place he demonstrated that the bactericidal property is not at all parallel to the agglutinative power, and this has further confirmed him in his opinion that there may be no direct relation between it and acquired immunity. He has found further that the power of the blood serum to destroy the typhoid coccobacillus is very variable in persons vaccinated by his method. After injections of large quantities of these killed bacilli this power may even be diminished for a very long period. On the other hand, medium or small doses of the vaccine first set up a negative stage, during which the bactericidal property is very feeble, and later they bring about an increase of this property, often very marked. Wright does not think that the bactericidal power can serve as the measure of the immunity acquired by the vaccinated individuals, but he hopes that some day a method may be found suitable for the examination of the blood which will give us information as to the degree of immunity conferred by the antityphoid vaccination. For the present the only basis upon which we can form any opinion on this subject is furnished by statistics. Now we know that it is often very difficult to collect data that are sufficiently exact. Hence during the war in South Africa, where one-fifth of the English troops, that is to say about 50,000 persons, were submitted to vaccinations by Wright’s method, it is only in certain cases that the statistical information can be utilised. Many of the patients attacked by slight fevers are omitted from the statistics, because from the absence of a precise diagnosis it is not known whether they should come under the category of typhoid patients or not. In other cases the secondary complications divert the attention of the doctors and prevent the registration of a proper diagnosis.

[Sidenote: [507]]

Of the data collected amongst the English troops in South Africa, Wright considers that those which were collected during the siege of Ladysmith were the most exact, on account of the facility with which it was possible to study and register all the cases of typhoid fever under these conditions of complete isolation. Now it has been recognised that, amongst the vaccinated soldiers and officers, there occurred scarcely one-eighth as many cases of typhoid fever as occurred amongst the unvaccinated (1,499 cases in 10,529 unvaccinated, and 35 cases in 1,705 vaccinated). The mortality amongst the vaccinated was also very much lower. The difference to the credit of the vaccinations should in reality be even greater, for amongst the unvaccinated are counted many persons who having already had an attack of typhoid fever were not submitted to vaccination.

The testimony of the majority of the medical men who followed the results of Wright’s method closely is also favourable to the vaccinations. Thus Henry Cayley[804] reports that the staff of a Scotch Hospital of the Red Cross, almost all of whom (57 persons out of 61) had received two vaccinal inoculations, escaped typhoid fever, in spite of the numerous opportunities afforded for the contraction of the disease. This very favourable example is also instructive in that it testifies to the value of two consecutive vaccinations. In many other cases where one has had to be satisfied with a single protective inoculation the results were less brilliant. According to Howard Tooth, who made his observations at Bloemfontein, the vaccinations according to Wright’s method must be regarded as very useful.

Outside South Africa this method has been employed on a fairly large number of persons in British India, in Egypt, and in Cyprus. According to the earlier statements from India the incidence amongst the vaccinated persons was one-third that of the unvaccinated. The most recent statistics[805] show still more favourable results. Thus at Meerut the incidence amongst vaccinated persons from Oct. 1899 to Oct. 1900 was one-eleventh that of the unvaccinated (2 cases of typhoid fever in 360 vaccinated, and 11 cases of the same disease in 179 unvaccinated): the mortality (one case amongst the former, six amongst the latter) was less than one-twelfth that of the unvaccinated.

In Egypt and in Cyprus according to the statistics communicated to Dr Wright[806] by Col. Fawcett these vaccinations have given even better results. In 2,669 unvaccinated persons there occurred 68 cases of typhoid fever with 10 deaths, whilst amongst the 720 vaccinated there was only a single case of this disease, this single case succumbing. Here, however, we have to do with a patient who must have received the vaccinal inoculation during the period of incubation, the disease breaking out soon after the vaccination. This would represent in all the cases a morbidity only one-seventeenth as intense amongst the vaccinated.

[Sidenote: [508]]

A few isolated voices only have not pronounced in favour of the antityphoid vaccinations and their opinion is formulated in a very undecided fashion. Amongst the most important of these adversaries, if indeed we may term them such, must be cited Washbourn[807], on account of his experience in microbiology. Attached as a doctor to the Yeomanry Hospital at Deelfontein in South Africa, he witnessed many cases of typhoid fever and was greatly struck by the death of two persons amongst the vaccinated patients. But he himself confesses that it is as yet premature to judge Wright’s method, and in support of his sceptical attitude does not offer any other satisfactory observation.

Outside the English colonies vaccinations against typhoid fever have been tried in Russia by Wyssokowitch[808]. He inoculated 235 soldiers of a regiment encamped at Kiew, amongst whom an epidemic of typhoid fever had broken out. The vaccinations were carried out by means of cultures killed with carbolic acid. We are unable to judge of the efficacy of the method because the number of persons vaccinated was too small and the epidemic too limited. It may be noted, however, that amongst these individuals not one took typhoid fever, whilst amongst the unvaccinated three cases of the disease were registered.

The antityphoid vaccinations have as yet only a very short history, and it is, perhaps, premature to express any decided opinion on the matter. We may, however, consider the results already obtained as offering encouragement to continue our experiments. Everything, indeed, tends to a recognition of the utility of vaccinations by means of killed typhoid cultures. The statistics are as a rule good; the danger from the protective inoculation is nil or quite trifling. With the exception of the discomfort of which we have spoken and which is transitory, no untoward result has ever been observed.

[Sidenote: [509]]

To all this must be added the fact that from the point of view of the pathogenesis of typhoid fever, all the probabilities point in favour of the vaccinations. Whilst in Asiatic cholera we have to deal with an intoxication, from the alimentary canal, an intoxication set up by vibrionic products, against which the subcutaneous inoculation of micro-organisms can not be effective, in typhoid fever we have to do with a real infection. The micro-organism, although developed at first in the small intestine, becomes generalised throughout the system. Thanks to improved methods it can always, or almost always, be found in the blood of the patient, and its constant localisation in the spleen furnishes a real evidence of this. Under these conditions it is quite natural to suppose that everything which is able to prevent the penetration of the typhoid coccobacillus into the blood and the internal organs ought at the same time to contribute to the protection of the individual.

We are fully aware that science has not yet said its final word upon this question. We are coming more and more to the conclusion that it is necessary to make two injections instead of one. It is possible that we may have recourse to certain improvements of the method by combining with it the injections of antityphoid serums as a protective measure. The near future will doubtless bring us the solution of these very important questions.

X. Vaccinations against human plague. Plague, which for so long was looked upon as the greatest scourge of humanity, has until recently remained almost unknown from the scientific point of view. But from the moment that it became possible to apply to its study the immense advances realised by microbiology the thick veil which had hidden its nature fell at a single stroke and science found itself in possession of effective means of fighting against it. Amongst these means one of the most important is protective vaccination.

[Sidenote: [510]]

When the last pandemic of plague broke out in Bombay and in the East Indies in general, Haffkine was there engaged in applying his method of vaccination against Asiatic cholera of which we have spoken in the preceding section. Well acquainted with the results of the bacteriological researches made on bubonic plague by Kitasato, and especially by Yersin, he, in 1896, began to study this disease. After the discovery made by Yersin, Borrel, and Calmette[809], who showed that animals susceptible to human plague could be easily vaccinated against the micro-organism which gives rise to it, Haffkine[810] endeavoured to find a practical method for the vaccination of man. He set up a laboratory at Bombay and, after some preliminary experiments on rabbits, he commenced to inject human beings with pure cultures of the plague coccobacillus. From 1897 up to the present he was able to vaccinate a very large number of individuals, and the results obtained have encouraged him to continue the application of his method. The principle of this method is that which had guided him in the preparation of anticholera vaccines and which is used for the vaccines against typhoid fever. It consists in the employment of pure cultures of the specific organism killed by heat. The cultures are grown in large flasks containing peptonised broth and sown with a small quantity of the plague coccobacilli. A little sterile butter or cocoanut oil is poured on the surface of the fluid. Under these conditions the organism grows abundantly and produces growths which hang down into the fluid, reminding us of the stalactites in a grotto. This mode of development forms one of the most typical characters of the micro-organism of human plague. The culture flasks are kept at a temperature of about 30° C. for five to six weeks, at the end of which period a large number of the bodies of the micro-organisms have fallen to the bottom of the flask, allowing much of their toxic contents to escape. The fatty layer on the surface favours a surface development of the coccobacilli, the number of micro-organisms in a flask being thus greatly increased.

After growing for 35 to 42 days under these conditions the cultures are heated at 65°–70° C. for from one to three hours with the object of killing all the micro-organisms and so rendering their injection innocuous. To make sure of the effectiveness of this heating care is taken to remove a small portion of the fluid and to sow it in a suitable medium. Should this medium remain sterile the vaccine may be used. Into adult men it is injected in a dose of 3 c.c., whilst women, children, and adolescents receive 2–2·5 c.c., into the subcutaneous tissue.

[Sidenote: [511]]

Some hours after the injection of the vaccine the temperature rises above normal, reaching 38°·5 to 39° C., and sometimes even 40°–40°·5 C. This febrile condition lasts from 15 to 48 hours. It is soon accompanied by pain, redness, and swelling at the point of inoculation. These symptoms persist for from three to five days. The malaise which follows the vaccinations is sometimes very uncomfortable or even painful, but never serious. Only in exceptional cases is the formation of abscesses observed, and this is due, undoubtedly, to contamination of the vaccines by foreign micro-organisms. The English Commission sent to India to study plague found other micro-organisms than the plague coccobacilli fairly frequently in the vaccine culture flasks, but, with very rare exceptions, these micro-organisms were found to be innocuous. By rigorously following the rules to be observed in making pure cultures it should not be difficult to avoid this complication.

Haffkine used every effort to induce his patients to be vaccinated a second time, being justly persuaded that two injections are capable of ensuring a more certain and more stable immunity than is a single injection.

[Sidenote: [512]]

From what moment immunity may be considered to be acquired has been a matter for great discussion. From very numerous experiments upon animals of various species, as well as many observations on man, it is now agreed that a period of several days (5–8) from the injection of the vaccine is required before immunity is manifested. It is for this reason that cases of plague which have broken out before this period has elapsed cannot be looked upon as contraindicating the efficacy of the method.

A large amount of evidence, coming from persons who have made their observations on the spot, is almost unanimous in endorsing the fact that Haffkine’s vaccination protects man against plague. It is often difficult to compile exact statistics in surroundings where so many factors contribute to deceive even the careful observer. In spite of this a certain amount of evidence has been collected which may be accepted as affording us fairly satisfactory information. One of the best groups of statistics was that collected at Damaun, a Portuguese possession in India, into which plague was imported from Bombay in 1897, and where a large number of vaccinations were carried out. From the report of Haffkine and Lyons[811], in a population of 8230 persons, rather more than one-fourth (2197) were vaccinated, the greater majority (6033) remaining uninoculated. Amongst the former only 36 died from plague, which corresponds to 1·6 per cent.; whilst amongst the unvaccinated persons the disease carried off 1482 persons or 24·6 per cent. Vaccination, therefore, according to these statistics, must have brought down the mortality to one-fifteenth. The German Commission[812], two members of which, Koch and Gaffky, went to Damaun to be present at the vaccinations and to observe their efficacy, pronounced in favour of Haffkine’s method. The English Commission[813] made reservations and criticised the statistics of Haffkine and Lyons (who amongst others attribute all the cases of deaths that occurred amongst the unvaccinated to plague), but in the end this Commission also recognised the utility of the vaccinations at Damaun.

The data collected with regard to the vaccinations at Undhera, Hubli, and several other places in British India confirm the results obtained at Damaun. The statistics collected at these localities are certainly open to criticism, but the result as a whole is none the less encouraging as regards this method of vaccination. According to the conclusions of the English Commission the “inoculations had a considerable effect in warding off plague attacks from the inoculated.... The protection afforded by inoculation seems, however, never to be absolute[814].” We do not, as yet, know the duration of the immunity produced by Haffkine’s vaccinations; it cannot be very long to judge from the experiments on animals, but it may last for several weeks, probably even for months.

The vaccinations by killed cultures may be especially useful when it is a question of limiting the extension of an epidemic that is already established. The ease with which the vaccine can be prepared renders it possible to obtain very large quantities of it in a short time, with which it is possible to immunise the entire population of towns or districts. But, as the immunity by this method requires several days for its development and as the injections of micro-organisms, even when killed, may be very injurious during the incubation period of plague or immediately before the infection, it is necessary to limit the vaccinations to persons who are not in intimate contact with the sick, or who are, from the beginning, exposed to infection[815].

[Sidenote: [513]]

Lustig and Galeotti[816] have described another method of preparing antiplague vaccine which can be utilised where it is of importance to obtain a large quantity of vaccine in a very short time. Instead of allowing the cultures to grow for five or six weeks as required by Haffkine’s method, the Italian observers make use of cultures on agar which have grown for two days only. The micro-organisms, removed from the surface of the agar, are treated with a weak solution of potash (0·75%–1%) which dissolves the bodies of the coccobacilli. This phenomenon has sometimes occurred by the end of twenty minutes, but it often requires an hour or more. The contact of the micro-organisms with the alkali must never exceed three hours. The viscous mass thus obtained is then treated with acetic acid, when a precipitate is thrown down. This precipitate, after being washed, is used for the vaccinations. When injected in large quantities into animals, Lustig and Galeotti’s product sets up necrosis, but a weak dose is well borne and confers immunity against plague. In man it is sufficient to inject two or three milligrammes of this substance diluted with water. The vaccinal nuclein of the Italian observers has been but little employed for the immunisation of man in India, but it is largely used in this country for the inoculation of horses from which to obtain an antiplague serum.

[Sidenote: [514]]

The serotherapeutics against human plague were inaugurated by the researches of Yersin, Borrel, and Calmette (l.c.), who demonstrated that animals susceptible to the plague bacillus can be vaccinated and even cured of experimental plague. The preparation of antiplague serum has since been energetically pursued under Roux’s direction at the Pasteur Institute. After several trials, some of which were very encouraging, others, on the contrary, somewhat unfavourable, they succeeded in obtaining a serum which is capable of curing plague after it has broken out and has become grave. As in this treatise we intentionally leave aside everything connected with healing we shall speak only of the antiplague serum as a protective agent.

Whilst vaccinations by killed plague cultures have been practised principally in the East Indies, the immunisation with antiplague serum has been employed in Europe, especially at the time of the epidemics of Oporto in 1899 and of Glasgow in 1900. In all these cases use was made of the serum from the Pasteur Institute, up to the present the most active of all those prepared. It is a serum obtained from horses treated for a long period with cultures of the plague bacillus and with the toxin of the same organism. Treatment is begun by injecting plague coccobacilli killed by heat (70° C.). These injections are made into the veins, with the object of avoiding the local lesions which are observed after the subcutaneous introduction of micro-organisms. When the horses have been rendered refractory by this treatment with dead micro-organisms, the next step is to inject (also into the veins) small quantities of living cultures. The doses of these cultures are gradually increased, and end by conferring upon the animal a very strong immunity, which is strengthened by injections of products of cultures passed through a Chamberland filter.

Calmette and Salimbeni[817] injected prophylactically more than 600 persons menaced by plague at Oporto. These comprised the doctors and the staffs of the laboratories of hygiene and of the disinfection services, the firemen who removed the sick persons and the dead, the families of those who were attacked, the members of the French colony, etc. Into each person 5 c.c. of serum was injected below the skin of the abdomen. These vaccinations in some cases caused nettle-rash, eruptions similar to those so often observed after the injection of the other kinds of serums. Of the total number injected two persons contracted plague: the unfortunate Doctor Camera Pestana and his assistant. The former succumbed to the disease, but the second only contracted a very mild form of it. The study of these 600 cases, as well as of experiments on animals, demonstrated that the immunity conferred by the antiplague serum is set up immediately after its injection but is not of long duration. It is probable that it lasts for 8 or 10 days, or at furthest a fortnight only.

Similar results were obtained at Glasgow. Van Ermengem[818], who has published a report on the epidemic in this town, mentions that more than 70 persons in good health were inoculated with the serum; each one received 10 c.c. beneath the skin of the belly. Of these 70 persons one was attacked with a fairly mild plague 8 days after the vaccination, and another, a housekeeper, was attacked, 9 days after the injection, with a congestion of the cervical glands induced by the plague bacillus. Both cases recovered. All the other vaccinated persons, in spite of constant exposure to the plague infection, remained unaffected. Van Ermengem was of opinion that the two persons treated with the serum were already infected when they were vaccinated.

[Sidenote: [515]]

The Belgian observer points out, further, the frequency of secondary accidents which were produced in the persons vaccinated at Glasgow. Van Ermengem himself went through the ordeal after being injected with 10 c.c. of serum as a protective measure and this gave occasion to several critics to attack the Pasteur Institute. This is how Van Ermengem himself puts the matter. “The accidents after the immunising injections ... were very numerous, they were observed 33 times in 72 cases. Sometimes they were even fairly serious, to the point of causing great suffering to the patient and of disquieting those around them. We could describe them from thorough knowledge, since we experienced them, but they scarcely differ from those which are observed from time to time after the injection of antidiphtheria serum, and, like them, they disappear without leaving the least trace” (l.c. p. 18).

In spite of these accidents and the necessity of renewing frequently (every ten or fifteen days) the protective injections of serum, their use is quite advisable in certain circumstances. They may render great service on board infected vessels or in lazarettos (as in the case which occurred at Frioul after the arrival at Marseilles of Arab stokers suffering from plague), in docks, warehouses, and stores where contaminated merchandise is found. They should also be employed to vaccinate those coming into immediate contact with plague cases in hospitals and in private houses. In a word, vaccinations by serum, owing to their power of conferring a very rapid immunity, should be practised wherever there is more or less immediate and imminent danger. Under these conditions they are of very great service in localising the disease.

The methods of vaccination against plague that have been employed up to the present may undoubtedly be improved. Calmette and Salimbeni (l.c.) have already published the results of experiments on animals undertaken with the object of studying the effect of a combined method of vaccination with antiplague serum and killed cultures of the plague bacillus. But even in their present form the methods used for protecting individuals against this disease deserve to be regarded as conferring great benefits on humanity.

[Sidenote: [516]]

XI. Vaccinations against tetanus. Tetanus unlike plague is not a contagious disease, nor is it capable of becoming epidemic. It constitutes, however, a very formidable disease against which all therapeutic methods have only a very limited effect. This is a further reason for drawing the whole attention of medical and veterinary men to the prevention of tetanus by vaccinal injections. Tetanus is a disease in which the intoxication plays an altogether dominant part. The tetanus bacilli do not develop, at the point where they are introduced into the body, unless favoured by auxiliary conditions, such as the multiplication of other micro-organisms. Even then the organism of tetanus reproduces itself with difficulty, and without becoming generalised throughout the body. The poison which it secretes is however sufficient to produce a very grave intoxication, ending most frequently in death. In certain countries tetanus, as a sequel to various wounds, is very frequently met with in man and in certain domestic animals, such as the horse, donkey, pig, etc.

It is only since the discovery by von Behring and Kitasato of an effective method of immunisation against tetanus that it has been possible to consider the practical application of antitetanus vaccinations. These observers demonstrated that the tetanus poison, when treated with trichloride of iodine, had its toxic action weakened and was transformed into an effective vaccine. Roux and Vaillard found that the addition of Lugol’s iodo-iodurated solution to the tetanus poison renders it capable of vaccinating all kinds of susceptible animals. It was shown later, that even with modified active tetanus toxin, we can still obtain good results when care is taken to inject the poison with great circumspection.

But it is not these vaccines obtained from tetanus cultures that have come to be used in practice. The best results are obtained by the use of antitetanus serums. After von Behring and Kitasato’s discovery of the power of the serum of animals immunised against tetanus to neutralise the action of the tetanus poison, very numerous experiments were made on the same subject. It has now become possible by treating horses with large quantities of tetanus toxin to obtain specific serums of extraordinary activity. Thus several serums are capable of preserving mice against a lethal dose of tetanus poison if we inject into them a quantity of serum equal to the one-thousand-millionth of their weight.

Serums of this strength protect domestic animals against tetanus. We know that many operations on horses, sheep, goats, pigs, and other mammals are very often followed by a tetanus which is usually fatal. Castration, amputation of the tail, the ablation of proud flesh or tumours, the operation for cryptorchitis or hernias, etc. are often complicated by tetanus. Moreover, tetanus may frequently appear in horses that have received wounds in the foot or in the lower parts of the limbs, “Clous de rue,” farrier’s punctures, wire-heels, blows, etc.

[Sidenote: [517]]

With the object of remedying this state of things Nocard[819] distributed to veterinarians about 70 litres of antitetanus serum to be employed for protective purposes. The majority of the animals treated (horses, donkeys, mules, bulls, rams, lambs, and pigs) received two injections of serum at an interval of 10–12 days, 20 c.c. for large animals and 6–10 c.c. for sheep and pigs. Of 3088 animals which received the first injection of serum immediately after the operation not a single one contracted tetanus. Of 400 animals which received the first injection at a later period, 1–4 days and more after the accidental wound of which they had been the victims, one horse only, treated five days after the accident (farrier’s puncture), was seized with mild tetanus, but it soon recovered. In the same localities where the results of the vaccination were so brilliant, 314 cases of grave and fatal tetanus occurred amongst animals operated upon or injured that were not submitted to the serum treatment.

It may be readily understood with these facts before us why the practice of protective vaccinations of animals against tetanus should have spread so rapidly amongst veterinarians. The demand for antitetanus serum from the Pasteur Institute of Paris for veterinary use increases every year at a great ratio. Thus in 1896 there were sent out only 1511 bottles of 10 c.c. each, in 1898 the number rose to 24,959 bottles, in 1900 it exceeded 43,000.

The efficacy of the antitetanus serum employed as a protective agent can no longer be questioned, but it must not be forgotten that its injection does not render the treatment of the wounds unnecessary. These wounds should receive a rigorous antiseptic cleansing. All foreign bodies should be carefully extracted; otherwise the prolonged presence of tetanus spores might set up a late tetanus after the disappearance of the transient immunity due to the serum.

[Sidenote: [518]]

The protective injections of antitetanus serum into men likely to contract tetanus are also beginning to spread. It often happens that bicyclists, in falling, receive injuries which are contaminated by horse-dung or other matters which may contain the spores of tetanus. In these cases, as in many other forms of injury, vaccination with antitetanus serum is indicated. Thus it happens from time to time at the Pasteur Institute that injured persons come and ask for a protective injection of serum. Several medical men and surgeons are now accustomed to vaccinate such of their patients as have had their wounds contaminated by earth or dung. All the cases of this treatment which have come to our knowledge have been followed by very good results.

XII. Vaccinations against diphtheria. Antidiphtheria vaccinations have been the subject of much discussion since the discovery of the antidiphtheria serum and its introduction into routine practice. A large number of works were published for and against the application of serum in protective treatment against diphtheria, especially in the early years of its use. Later the controversy has subsided somewhat, and at present very few writers are found who continue to decry antidiphtheria vaccinations.

The antidiphtheria serum was discovered in 1890 by von Behring working in collaboration with Kitasato; these observers demonstrated in laboratory animals its neutralising action upon the diphtheria toxin. A little later von Behring began to apply it in the treatment of diphtheria, but the early results were far from satisfactory, and von Behring soon recognised that it was necessary to obtain much more active serum. Along with Ehrlich of the Institute for Infective Diseases at Berlin he set to work to study this problem. In collaboration with several investigators, among whom I may cite Wernicke, Wassermann, and Kossel, he succeeded in obtaining very encouraging results as regards the antitoxic strength of the serums and their therapeutic action on children attacked by diphtheria.

At this time, also, Roux in Paris began, assisted by Martin and Chaillou, to study the same question. These observers prepared serums which for that period were very active and made a very effective application of them upon more than 300 diphtheria patients.

From the year 1894 the use of serum began to spread in all countries, and it was then that an attempt was made to apply it to the protection of children in good health, but who had been specially exposed to contagion.

[Sidenote: [519]]

It was necessary to have at command large supplies of antidiphtheria serum; this was prepared by injecting into horses repeated doses of the toxin manufactured by the diphtheria bacillus. The serums thus obtained were first tested as to their protective, antitoxic, and curative action on guinea-pigs, animals very susceptible to diphtheria. The necessity of finding some means of measuring the strength of the serum soon arose. Von Behring and Wernicke at first standardised it on the basis of the number of grammes of guinea-pig which could be protected by one gramme of serum. Later, von Behring[820] introduced the principle of the “normal serum,” that is to say, a serum of which 0·1 c.c., mixed with 10 lethal doses of diphtheria toxin, is capable of preventing every morbid symptom in a guinea-pig weighing 300 to 400 grammes.

Ehrlich[821] perfected this method in the following way: to tubes, each containing 10 lethal doses of a standard toxin, are added different amounts of serum. These mixtures are brought to the same volume of 4 c.c. by the addition of physiological saline solution, and each is immediately injected below the skin of a guinea-pig. If 0·1 c.c. of a serum completely neutralises the 10 lethal doses of toxin, the serum retains its name of normal serum; in the case where 0·05 c.c. is sufficient to bring about the same result the serum is designated double normal serum. When 0·001 c.c. gives the same results, a hundred times normal serum, and so on. A cubic centimetre of normal serum (that is to say a dose capable of neutralising 100 lethal doses of standard toxin) constitutes an “immunising unit” (Immunisirungseinheit (I.E.) of Ehrlich). As it was soon recognised that toxins, even when kept under the best conditions, lose more or less of their toxic power, Ehrlich had to modify his method of standardising serum. He now makes use of a standard antidiphtheria serum, kept in a dry condition, which is much more constant than are the toxins. Solutions of this standard serum are prepared and compared with the serum whose strength has to be determined. Ehrlich has given a detailed description of the method of procedure required to obtain exact results.

[Sidenote: [520]]

At the Pasteur Institute Ehrlich’s method has been adopted, supplemented however by another test for the estimation of the strength of antidiphtheria serums, a method allied to von Behring’s old method. Various doses of the serum to be examined are injected subcutaneously into guinea-pigs, and 24 hours later these guinea-pigs receive a quantity of a living culture of diphtheria bacilli which kills control animals in 30 hours. The protective power of the serum in relation to the weight of the animal is thus determined. For example, a serum which is said to be active at 1/100,000 has the power, in a quantity equal to 1/100,000th of the weight of the inoculated guinea-pig, of preventing a fatal result. It was thought, at first, that the protective power, measured in this way, would be proportional to the antitoxic property determined according to Ehrlich’s method. But as the results given by these two methods were often widely different, it was resolved at the Pasteur Institute to examine by both methods all the serums intended for use in practice. This led to the conclusion formulated by Roux[822], in his report communicated to the International Congress of Hygiene, held at Paris in 1900, that a serum possessing a very high protective power (against the living diphtheria bacillus) might be only feebly antitoxic, and vice versâ.

[Sidenote: [521]]

This result is explained by the fact that the antidiphtheria serums are very complex fluids, containing several superposed properties of very variable strength. Marx[823], of the Frankfort-on-Main Institute, tried to shake Roux’s conclusions, bringing forward his experiments made on guinea-pigs and rabbits injected with antidiphtheria serum into the peritoneal cavity and into the veins. He wished in this way to avoid the introduction of the serum into the subcutaneous tissues, whence the absorption of the antitoxin must take place in a very irregular fashion. In Marx’s experiments, thus carried out, the protective power of the serums was always found to run parallel with their antitoxic power, from which he concluded that Roux’s view was incorrect. It must not be forgotten, however, that this view was founded on experiments in which the antitoxin had been injected into the subcutaneous tissue before or simultaneously with the toxin or the diphtheria bacillus. Under these conditions the protective power is often found to be altogether disproportionate to the antitoxic power. This fact has been observed so carefully and with such exactness that it is impossible to deny it. Now it is undoubted that the conditions of the experiments upon which Roux relies correspond much more closely with those that are realised in vaccination of man against diphtheria than with the conditions met with in Marx’s experiments. In these vaccinations antidiphtheria serum is injected below the skin of persons whom it is wished to protect against the action of the diphtheria bacillus.

With the object of bringing about a unification of the methods of estimating serums used in different countries the International Congress of Hygiene, held at Madrid in 1898, appointed a special Commission to settle this problem. But when the Congress met again at Paris in 1900 this Commission had not completed the task allotted to it. The representatives of the various methods had exchanged ideas, but in applying the same method the results obtained in various places and by various observers presented differences too great to allow of any understanding being arrived at. It is evident that we have here a very complicated problem. The serums are tested on living animals in which of course nothing like the constancy of a chemical reaction can be obtained.

Possibly the methods of breeding and the races of the same animals in the different countries may be quite sufficient to explain the divergencies in the results obtained. Whatever may be the reason the unification of serum estimation has not yet been obtained, and it is difficult to anticipate that any better result is to be arrived at.

From all this we may draw the conclusion that the possibility of attaining a too rigorous precision in the standardisation of serum has been exaggerated. Our object must be to obtain results as favourable as possible in the application of the antidiphtheria serums, and for that purpose it is necessary to inject greater quantities than those which may be indicated by any method of estimation. This rule is applied as far as is possible at the Pasteur Institute.

As regards vaccination against diphtheria of persons who are in good health but are especially exposed to infection, the question must be accepted as settled in the affirmative.

[Sidenote: [522]]

From the commencement of our attempt to cure diphtheria by means of a specific serum, the necessity was seen of protecting children who were in contact with the sick persons against this disease. Small quantities of serum were injected into such children for protective purposes. The first results communicated in 1894 by Roux to the Congress at Budapest being very encouraging, an attempt was made to give the greatest possible extension to the system of vaccination by antidiphtheria serum. In the following year, 1895, fairly numerous statistics had been collected, and Torday[824] at Budapest, Kurth[825] at Bremen, and Rubens[826] at Gelsenkirchen were able to publish a number of favourable statistics. Soon afterwards, however, a fatal case occurred in the family of a well-known Berlin doctor, Langerhans[827], an accident that started a violent controversy and stirred up an active campaign against serum. Langerhans’s son, a boy aged 2 years, in good health, was inoculated with a small dose (1·2 c.c. of this serum) and succumbed about a quarter of an hour afterwards with symptoms of suffocation. The post-mortem examination made by Strassman[828] showed the cause of death to be suffocation in consequence of the aspiration of food into the respiratory passages during the act of vomiting. An examination of the serum used by Langerhans did not reveal any toxic action on animals or any contamination by micro-organisms. All to no purpose, the serum was held answerable for the death of the child, and an attempt was made to demonstrate at almost any cost that its use in human practice was extremely dangerous. Gottstein[829] joined in chorus with the over-excited opinion and published a denunciation of vaccinations by antidiphtheria serum. He collected from the literature of both hemispheres four cases, in all, in which death had occurred some time after the injection of this serum into children not suffering from diphtheria. A perusal of the description of these cases is sufficient to convince one that the death could in no sense be attributed to the serum, and that it could be explained much more easily by the fatal action of the streptococcus, the cause of the non-diphtheritic affections of the children that died.

[Sidenote: [523]]

The ineptitude of this denunciation must have done much to calm public opinion, and in September of the same year, 1896, C. Fränkel[830], in a report presented to the German Association of Public Hygiene, was able to give a review of the state of the question of vaccination against diphtheria, summing up in favour of the use of the specific serum. “Taking into consideration the data collected,” he remarks, “it is scarcely possible to doubt the value of immunisation by serum, so that we may say positively that we are now treading a path which will lead us to great and important results.” This very favourable opinion was due in great measure to the vaccinations carried out in the wards of Heubner’s Clinic at Berlin[831]. At first, injection of the antidiphtheria serum as a protective into patients who were found in the immediate vicinity of the children attacked with diphtheria (contacts) was deemed to be sufficient: but in consequence of the results obtained by this method it was decided (starting from January, 1896) to inject all children who came into the hospital. During the first period there still occurred a few cases of diphtheria contracted in hospital, but from the moment systematic and general vaccinations were introduced not a single new case occurred.

The immune condition of the vaccinated children is maintained for three to four weeks. After this lapse of time some of them contracted diphtheria. But it was sufficient to introduce revaccination at the end of this period to prevent the outbreak of any further case of diphtheria in Heubner’s wards. Results quite as favourable and as convincing were obtained in the department for children attacked by scarlet fever.

[Sidenote: [524]]

The amount of serum injected varied, but it was usually given in doses of 1 c.c. containing from 200 to 250 I.E. (immunising units of Ehrlich). The serum was always found to be innocuous except in certain cases where it set up erythemata of greater or less extension. In 460 injections 20 cases of these exanthemata were produced, that is to say 4·34%. The frequency of these complications was not proportional to the amount of serum injected. According to the figures communicated by Löhr the largest doses of the serum employed did not produce exanthemata more frequently than did the smaller quantities. Thus 117 injections of 1 c.c. only were followed in five cases by these erythemata, which corresponds to 4·27 per cent. The hope of diminishing the frequency of the exanthemata by diminishing the amount of serum injected was therefore not realised. This fact lends support to the conclusion above formulated as to the exaggeration of the importance of the measurement of serum. If it could be established that small quantities of serum rich in antitoxin caused cutaneous eruptions less frequently than did stronger doses there would certainly be a great advantage in using serums containing a very large number of immunising units for vaccination. Perhaps serums having a great antimicrobial power but of comparatively low antitoxic potency might even render great service in protective treatment. Future researches undertaken in this direction alone can give us information on this subject.

In 1896 the vaccinations in Heubner’s wards were discontinued, but the reappearance of diphtheria in 1897[832] rendered their recommencement necessary. 500 children were vaccinated each with 200 immunising units. Following this no case of diphtheria broke out. The eruptions were rare and slight.

The increasing extension of the use of antidiphtheria serum for the cure of the disease after it has broken out has led to a greater development in its use as a preventive measure. Thus, in the countries where diphtheria is endemic, vaccinations by serum are now practised very extensively. In Russia, which is one of the great hotbeds of this disease, vaccinations by antidiphtheria serum are frequently practised.

[Sidenote: [525]]

At the Congress of Russian doctors at Kasan in 1896, Vissotsky communicated the result of 2,185 vaccinations which gave a morbidity of 1·3%, a morbidity that must be regarded as very low indeed. A well-known Russian physician for children’s diseases, Rauchfuss[833], who cites these figures, has collected several other facts concerning the prophylactic injections of antidiphtheria serum followed by good results. In the government of Woronetz, according to the statements of Ouspensky[834], out of 738 vaccinated persons diphtheria occurred in 2·2 per cent., which again may be considered a favourable result, especially if we take into account the great extension of diphtheria in this country. In Podolia, out of 537 children vaccinated in 1895, only four cases of diphtheria occurred, a morbidity of 0·74%. In the government of Kherson, one of the great centres of diphtheria in southern Russia, the results appear to be less favourable: out of 543 children which received a protective inoculation, 21 contracted the disease (or 4·6 per cent.), of which five died. If we study these statistics more closely[835] it will be seen that these results are far from being unfavourable. The protective inoculations were made only once and with somewhat small doses, nevertheless many of the cases of diphtheria broke out only at a late period, sometimes more than nine months after the injections had been made. Now, it is proved that these injections, although very efficacious, produce their action for a very short time only, for a few weeks at most. Of the five fatal cases, four did not occur until 2, 4½, 6, and 9½ months respectively after the protective inoculation. It is impossible to look upon these statistics as affording proof of the inefficacy of the serum. The fifth case is the only one that occurred within a short time (15 days) of the injection, and in this instance only 150 immunising units had been injected.

A detailed study of the other examples of antidiphtheria inoculations in the government of Kherson leaves a very favourable impression. Out of 90 children inoculated by Wecker[836] in the district of Elisabetgrad not a single one contracted diphtheria, which is the more remarkable as at the time of the inoculations there existed in the same families 14 cases of diphtheria; the chances of contamination were thus great.

[Sidenote: [526]]

Recently, on the occasion of the outbreak of a great epidemic in Paris, the question of vaccinations by serum was again raised and earnestly discussed at the Paris Hospitals Medical Society and at the Society for the Study of Children’s Diseases. Voisin and Guinon[837] communicated the history of an epidemic amongst the staff at the Salpêtrière Hospital in the wards of idiot children, “against which protective serum treatment was remarkably effective and absolutely innocuous.” The serum was injected, in the case of children more than 10 years of age, in 10 c.c. doses, and into the rest in 6 c.c. doses. This measure brought about first an abatement and then cessation of the epidemic. The immunity after a single injection lasted from two to three weeks, and the few cases of diphtheria which broke out amongst the infected children were distinguished by their great mildness. Erythemata and other post-injection complications were insignificant, so that the protective use of the serum was fully justified. Only a small minority of the medical men who took part in the discussion spoke against the antidiphtheria vaccinations; once, indeed, a reference was made to the case of Langerhans’s child, although its death was certainly not due to the serum. It is true that in families where it is possible to keep the children under careful observation and to intervene at the appearance of the first symptoms of diphtheria, the preventive injections may be dispensed with, but in practice these favourable conditions are rarely realised, and the prophylactic serum treatment is then of great service in preventing the outbreak of the disease.

Netter[838] communicated to the Society of Pediatrics a summary of 32,484 observations on the prophylactic injection of antidiphtheria serum. Of this number 192 cases were noted in which the diphtheria broke out in spite of the injections, corresponding to 0·6 per cent. of those treated. These figures, however, included all cases of the disease which occurred up to thirty days after the injection. Now, the immunity is often less durable than this, and it may disappear more or less completely twenty days and sometimes even fifteen days after vaccination.

Netter himself made great use of antidiphtheria vaccination. It was his custom to propose to the parents either a protective inoculation at once or a systematic precautionary bacteriological examination of the throats of the children not yet attacked. He regards the first method as preferable. According to the latest statistics which he was kind enough to communicate to me, of 152 children (in 50 families), 91 of whom received protective inoculations, not one contracted diphtheria: whilst in 239 other families where the children had not been inoculated there were 52 cases of diphtheria, with 10 deaths. Many practitioners in Paris have now pronounced themselves in favour of protective injections of the serum, and the Society of Pediatrics, at its meeting on 11th June, 1901, concluded the discussion of this question by proposing the following resolution: “The Society of Pediatrics, affirming that protective inoculations present no serious danger and confer a very considerable amount of immunity for some weeks, recommend their use when children are gathered together in numbers, and in families where a scientific supervision cannot be maintained.”

The large amount of evidence collected on this question leaves no doubt as to the real efficacy of vaccinations by antidiphtheria serum.

[Sidenote: [527]]

The summary of the results obtained by vaccination in the 12 diseases of man and of animals I have just placed before my readers cannot pretend to serve as a detailed guide to prophylactic practice. My object has been merely to concentrate into one chapter the principal data upon which this very important question rests, to bear witness to the progress which has already been realised, and at the same time to show that the scientific study of immunity is in very intimate relation with its practical application. It is evident that the road is far from traversed to its terminus, for there are many infective diseases in which vaccinations cannot be employed, but it is none the less certain that the path which has led to so many important and useful results should still be followed in studying problems which up to the present we have been unable to solve.

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