A manual of bacteriology

Front matter

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Preface To The Fifth Edition

In the preface to the second edition of this manual the author states that: “the purpose of this book is to give in the smallest possible space the facts which a physician must know, with some of those which it is desirable that he should know, and a little of that which he may learn if his needs or inclinations lead him to go further.’’ While n the present edition this purpose has been kept in mind by the reviser, nevertheless it has been necessary to make many alterations in order to place the work abreast of the progress which has been made since the publication of the last edition. Some things which have become obsolete have been omitted, much that is new has been added, and the scope has been somewhat widened.

Since the book is designed primarily for medical students, the method of expression, as in former editions, is often more definite than is perhaps justifiable, and it must be understood that this form is adopted merely in order to make a clear presentation of the subject, not that the matter is in every such case finally settled, nor that the views as stated are necessarily shared by the author or the reviser, but that they are held by those whose opinions are worthy of consideration, and are the interpretation of the results of painstaking investigation, but which, nevertheless, may be in time modified or abandoned as a result of further research. :

Those who are familiar with the former editions of the book will find that the arrangement of chapters is the same as heretofore. Many references to the literature have been added,

Vv vi PREFACE.

but these are by no means exhaustive, many had to be omitted with regret. The hygienic examination of milk has been practically rewritten; the hygienic examination of water considerably expanded. The chapter on disinfectants, and that on surgical antisepsis have been also greatly altered. The interesting theoretical subject of the diversion of complement has been added to the chapter on immunity. The irypanosomes and the amebe have been given additional space, but certainly not more than these increasingly important microorganisms demand. The index has been not only greatly enlarged, but the references have been made much fuller and more specific.

A very full card catalogue of references prepared by Dr. Williams was made use of in looking up most of the articles which have been cited.

As in the fourth edition, the author is relieved of all responsibility for the statements made in the present edition; both for those retained from former editions, as well as for those which have been added by the reviser.

B. MEavE Botton.

WasHINGTON, D. C.,

Preface To The Third Edition

The plan used in the preceding editions of this manual has been followed in the preparation of the present one. The only departures have been in the insertion of a short historical sketch and the freer use of references to original articles and reviews. It is hoped that these features will assist in arousing the interest of students. As far as possible, reference has been made to articles in American and English journals likely to be easy of access. Besides the ones just named, numerous additions have been made which the recent advances in our knowledge have rendered necessary. Most of the illustrations of apparatus are new. The photomicrographs also are new and original, with a few exceptions noted in the text. It is probably needless to say that none of them were retouched. The writer is indebted to the Gratwick Laboratory, of Buffalo, for the use of its facilities in making these photographs. H. U. W.

BurFraLo, NEw York, August, 1903.

vii

Contents

PAGE Introduction with Historical Sketch. . . fe aS hi ele las bdo PART I.

BACTERIOLOGICAL TECHNIC.

Chapter I

Examination of Bacteria with the Microscope, NS Methods of StaMinge ca RS a ae aL 18 CHAPTER II Sterilization: «6. 64% a bw es ear Gh IAC Tae Ge ee be 53 CHAPTER II Culture-media . Bo es eg Se te 6 ‘ : 64 CHAPTER IV.

The Cultivation of Bacteria. Tube-cultures; the Incubator; Anaerobic Methods. . . ee nee ee eee : 78 CHAPTER V.

The Cultivation of Bacteria (Continued). Isolation of Bacteria; Plate- Cultures’ 2) ek a ee ee are : 94

CHAPTER VI.

Inoculation of Animals. Autopsies; Collodion Sacs .... «.. . 102

CHAPTER VII.

Collection: of .Miatetial s.. is a. wg ee oe a Re ge eR . 107

CHAPTER VIII.

Systematic Study of p epeers of Bacteria. Suggestions for Class-work; RRulesiy iA cas ata a a he ee eS Se -ee ee a G Se 112 x CONTENTS.

Part II

EXPERIMENTAL STUDY AND PRACTICAL APPLICATIONS. CHAPTER I.

PAGE Classification; General Morphology and Physiology of Bacteria » BIZ CHAPTER II.

Products of the Growth of Bacteria 128 CHAPTER III.

Bacteria of Soil, Air, Water and of Milk and Other Foods 135 CHAPTER IV.

Bacteria of the Normal Human Body. . . ‘ 160 CHAPTER V.

Bacteria in Disease a ae ee ee ce 167 CHAPTER VI.

Bacterial Poisons; Agglutinins; Lysins; Precipitins..... . 4 186 ; CHAPTER VII.

Immunity; Phagocytosis; Antitoxin ab rae & i i . 198 CHAPTER VIII.

Disinfection, Sterilization and Antisepsis . s : . 238 CHAPTER IX.

Surgical Antisepsis 262 PART Ill.

NON-PATHOGENIC BACTERIA . . 267 PART IV.

PATHOGENIC BACTERIA . . dus Be oh 282 PATHOGENIC PROTOZOA Sa oe BOY APPENDIX. . . my a 426

INDEX . i ee a 438

LIST OF ILLUSTRATIONS.

. Micrococci, Bacilli, Spirilla . : . Test-tube with Culture-medium..... . Microscope. .......

. Abbé Condenser

. Platinum Wires... .....

Hanging-drop .

Cornet Forceps for Cover-glasses .

. Stewart Forceps for Cover-glasses . Kirkbride Forceps for Slides . . . Schanze Microtome

. Hot-air Sterilizer

. Arnold Steam Sterilizer ok . Massachusetts Board of Health Stetilizer eons . Koch Steam Sterilizer .

. Autoclave .

. Kitasato Filter

. Test-tube with Potato é : . Wire Basket for Test-tubes . . .

. Manner of Holding Test-tubes

. Stab-culture . Bia 6

. Smear-culture

. Incubator .

. Reichert Gas-regulator

. Gas-regulator, mercurial

. Roux Bimetallic Gas-regulator .

. Koch Automatic Gas-burner . 58 . Rogers’ Electric Thermo-regulator. . . . . Buchner’s Method for Cultivating Anaerobes

. Frankel’s Method for Cultivating Anaerobes . . . . Novy’s Method for Cultivating Anaerobes . Streak Culture of the Potato Bacillus. . . Petri Dish

. Dilution-cultures in Esmarch Roll- tubes. A a of Colonies on Gelatin in a Petri Dish xi xii LIST OF ILLUSTRATIONS.

FIG. PAGE 35. Esmarch’s Roll-tube OS, Bab Teak ce wr SiS Seo Wee «hay Ge Se ‘ 99 36. Mouse-holder «2... ee ee + 102 37. Apparatus for the Subcutaneous Insertion of Solid Substances . 103 38. McCrae’s Method for Making Collodion Capsules... . 106 39. Cover-glass Preparation of Blood . .. 1. +s sees 108 40. Sternberg Bulb RRS Bo ee Gale pee es . Log 41. Micrococci of Various Forms... 1... ee ee . 118 42. Bacilli of Various Forms . foe gn ty Be ee 119 43. Spirillaof Various Forms . ...-:+:+-> A ee ‘ 119 44. Involution Forms . . hy wey Miche deters al eae Se é . 120 45. Bacteria with Capsules ey ei RO A ie HS A 122 46. Bacteria with Spores elahel Ab ayes hewn “nk2g 47. Bacteria Showing Flagella. . . 2 7 ee ee se 24 48. Fermentation-tube . . oa é < ‘ fo Real EB2 49. Sedgwick- Tucker Aerobioscope 2 RR ee we 238 50. Receptors of the First Order Uniting ith Tesn Rerare 219 51. Receptors of the Second Order and of Some Substance Uniting with One of Them .. . 220 52. Receptors of the Third Order il ‘ef Some Gubuiance Unite with One of Them .. . - 8222 53. “Spectrum”? of aheaveticalliy Bash Guide Powis : rear . 224 54. “Spectrum” of Very Fresh Crude Toxin . . 225 55. “Spectrum” of Crude Toxin as it is Supposed Always Peactically to OCeur oS aoe ss Pa : 2 A 225 56. Mechanism of Bacteriolysis. . . . ‘ . 230 57. Diversion of Complement in Undiluted means Serum. . . 233 58. Partial Bacteriolysis,etc. . ... i. 8 é . 234 59. Bacillus subtilis . ‘ . ‘ . 272 60. Spirilla from Swamp Water. ...... ee ae 275 6r. Spirilla from Swamp Water with Flagella. . ... .. « . 276 62. Yeast Cells... . . 278 63. Penicillium glaucum, Oidium lactis, Agpevsillas Bivens bor mucedo . 3 : a ae: ‘ 279 64. Staphylococcus pyogenes aureus in Bus hte xe ; 289 65. Staphylococcus pyogenes aureus in Pure Culture. . . jet ZOE 66. Staphylococcus pyogenes aureus in Culture in Gelatin ..... 299 67. Streptococcus pyogenes, Pure Culture. . . ‘ : . 296 68. Streptococcus pyogenes in Pus . 5 , 5, at . « 9 BOF 69. Streptococcus pyogenes Culture on Aga Hee area 298 yo. Micrococcus tetragenus in Pus... . : 299 71. Micrococcus lanceolatus (of Pneumonia) in 7» Souci ba of 304 72. Micrococcus lanceolatus (of Pneumonia) Showing Capsules + 305

73. Diplococcus intracellularis meningitidis. . . . . 3 + 309

LIST OF ILLUSTRATIONS.

. Gonococcus in Pus . Bacillus pyocyaneus de . Bacillus of Bubonic Plague... .... 2... . Bacillus aerogenes capsulatus... . .

. Bacillus aerogenes capsulatus Culture.

. Bacillus of Tetanus... 2... 2... bc AG 2 ». Bacllissob Anthrax. 2. 4. 4.9 a 44 8 4 Ye wx . Bacillus of Anthrax with Spores... ... ae . Bacillus of Anthrax Colony .......... . Bacillus of Anthrax Culture... ....... . Bacillus of Anthrax Showing Concave Ends. . . - Bacillus of Anthrax in the Liver... ..... . Bacillus of Diphtheria. . .......... . Bacillus of Diphtheria, Neisser’s Stain se Cats, sta oe . Tubes for Cultivation of Diphtheria Bacillus... . . Bacillus of Diphtheria, Culture. .. 2... .

. Bacillus tuberculosis. . 2... 00... 000 . Branching Form of Tubercle Bacils .

. Bacillus tuberculosis, stained, in Sputum. . Ray-fungus of Actinomycosis, Fresh Preparation . . . Actinomyces bovis from a Pure Culture. . . . . . Bacillus of Typhoid Fever. . . «2... . Bacillus of Typhoid Fever with Flapella ae apes oes . Widal Serum-reaction with Typhoid Bacilli. . . . Bacillus colicommunis. ........... . Bacillus coli communis with Flagella .

. Spirillum of Cholera... 2... 2... 3

. Spirillum of Cholera Involution Forms... . . . Spirillum of Cholera Colonies on Gelatin Plates . Spirillum of Cholera Culture in Gelatin. ... . Vibrio proteus... . ....e ete, cher 38 . Spirillum of Relapsing Fever... ....... . Malarial Parasite... ...... . Malaria] Parasite... .

. Malarial Parasite... . cA ar ie . Malarial Parasite... 2... we ee ee . Trypanosomes in the Blood of the Rat . . . Plates for Counting Colonies.

eee 403

. 417 . 417 - 417

APR ee a AT

421 440, 441, 442

Introduction

BACTERIOLOGY is not a subject which one should attempt to learn from books alone or without instructors; for aside from the difficulty or impossibility of such a task, there may be danger as well. Indeed the warning should perhaps be given in the beginning that in view of the fact that so many bacteria cause diseases which not only affect the individual who suffers, but makes him a menace to those about him, no one is justified in entering upon the study without proper guidance.

Anyone who has not himself worked in a bacteriological laboratory finds it difficult to form a vivid conception of what bacteria are like, because among the familiar animals and plants there are none with which a close comparison can be made. Of the common organisms, perhaps ordinary yeasts and moulds are most like the bacteria. Yeasts and moulds, as everyone knows, grow on bread, cheese, meat, syrups and the like. They flourish in moist and dark places, as do mushrooms, puffballs and the other fungi. All these fungi, appearing so different in some respects, are alike in one particular, which is the absence of the green color that we are apt to think of as being the essential feature of vegetation. Plants that are green owe their color to a substance called chlorophyll. Upon the properties of this substance one of the most fundamental vital phenomena in biology depends. By means of chlorophyll, under the influence of sunlight, plants are able to use as food the carbon dioxide which is always present in the atmosphere in small amounts. Although carbon dioxide is one of the simplest and most stable of compounds, its component elements are dissociated by the plant, and employed in

I the formation of other much more complex and unstable compounds, such as starch and cellulose, which enter into the plant’s structure. The work of plants, it will be noticed, is in the main, precisely the reverse of that performed by animals. Animals take the unstable carbohydrates with high potential energy, such as starches and sugars, as food, and exhale the stable carbon dioxide from the lungs. At the same time the animal receives the benefit of the energy resulting from the oxidation of the carbohydrates, which may appear indirectly in the form of nervous or muscular activity or warmth.

Those plants that are devoid of chlorophyll are compelled to some extent to use the same kinds of food as animals. They are unable to decompose carbon dioxide (in most cases), and procure their nourishment from substances derived from the dead or living bodies of other plants or animals. Since they have no chlorophyll, light is of no advantage to them, and is often a positive detriment. Bacteria contain no chlorophyll, and consequently are unable to decompose carbon dioxide and to use it as food.*

There is another well-known property, possessed by yeasts especially, which may be useful in explaining the work done by bacteria. It is a fact of every-day observation that alcohol and gas are formed when ordinary yeast grows in fruit juice or other fluids containing sugar. It not only appears that bacteria sometimes form alcohol and gas from sugar, but that with different kinds of bacteria and different kinds of food material a great number of substances are formed, some of which are powerful poisons. In most, if not in all, of the diseases caused by bacteria such poisons are produced within the living body of the affected individual, and the symptoms of the disease and the changes produced in the body are certainly due to these poisons, as a rule, rather than to the direct action of bacteria.

On account of their extremely minute size, the bacteria can-

* See Part II., Chapter I.

not be seen as individuals without the aid of the microscope, although great numbers of them taken together may form a plainly visible mass of growth. When they are examined with the microscope they appear as little, round, rod-shaped or curved bodies, which may be likened to so many periods, dashes and commas. It is at once perceived that each bacterium is an individual by itself, and that it consists of a single cell, not of an aggregation of cells, as do most of the common plants and animals.

Under favorable conditions bacteria undergo rapid multiplication. The individuals in some forms divide into two cells, in other forms into four cells, in others again into eight cells simultaneously. The process takes place by direct cell division, and is called fission.

Under certain conditions, bright, glistening bodies make their appearance in certain bacteria, and become larger and larger, while the cells in which they develop break up into fine fragments. These bodies are called spores, and represent a resting stage in some respects resembling the seeds of higher plants. They have much greater resisting power against injurious influences than is possessed by the growing or vegetative forms. There are spores that can withstand boiling for hours, but fortunately that it not true of the spores of any of the bacteria that produce disease, as far as is yet known. The earlier investigators observed the appearance of bacteria in nutrient infusions which they had endeavored to sterilize by heat. They looked upon this fact as indicating the possibility of spontaneous generation, and it furnished the chief support of that theory. Probably their infusions contained very resistant spores, and were in reality not sterile.

Definition.—F rom these facts a definition for bacteria may be formulated.

Bacteria (Greek faxripwor, meaning a little stick) are extremely minute, unicellular plants, which have no chlorophyll, and which divide by fission. They are sometimes called schizomycetes. In every-day language they are known as microbes and also as germs. They are generally classed with the fungi. In some respects they seem quite closely related to the alge or simplest green plants, and, on the other hand, they have strong points of likeness with some of the unicellular animals belonging to the infusoria.

Bacteria are divided into two great groups:

I. The lower bacteria include those forms which are of most

iz ww ‘importance at present, from a medical

ar ee a=" ts) and economic point of view, and conwest ee sist of:

Cocco-bacilli—mostly short, thick, oval forms which also occur in rods.

Micrococci, or cocci (singular, coccus)—spherical forms.

Bacilli (sing., bacillus)—long and straight, or rod-shaped bacteria.

Spirilla (sing., spirillum)—consisting of spiral filaments like the turns of a corkscrew, or parts of spirals shaped like commas.

IJ. The higher bacteria, which consist of long filaments made up of segments more or less united. In some of these the filaments show dichotomous branching. This group is more fully discussed under the non-pathogenic bacteria, Part III. A few of them are pathogenic.

The extreme smallness of the bacteria is hard of comprehension. We may say, of most of them, that from 5,000 to 25,000 placed end to end would make a line about an inch in length. The tiny speck which adheres to the end of a fine platinum wire when this is used to obtain preparations from cultures is found upon examination with the microscope to consist of many thousands of bacteria.

It is well known that bacteria are present on most of the objects about us. They occur on the skins of men and other animals as well as in the mouth, stomach and intestines, and

Micrococci. Bacilli. Spirilla.

Fic. r.

on most of the surfaces of the body that open to the external world. They are found in the water of rivers and lakes and in the ocean. They appear in the soil down to a depth of several feet. They float in the air, except at high altitudes and over the ocean. Nansen found bacteria on the ice of the Polar sea. Investigators have even reported finding them fossilized, indicating, as we might expect, that they existed at remote periods in the earth’s history. But the vast majority of them are entirely harmless so far as we are concerned, and many of them are indispensable in maintaining the balance existing between dead matter and living beings.

Were it not for the putrefactive and nitrifying bacteria, the dead bodies of plants and animals would lie practically unchanged where they fall, and the fertilization of the soil necessary for the life of most plants, by means of substances derived from such dead material, would cease.

Some kinds of bacteria are useful in taking nitrogen from the atmosphere, and making it available as plant food in the soil, and are thus employed in the place of chemical fertilizers. Many of them have been made to subserve a useful purpose in the ripening of cream and cheese, and in the manufacture of vinegar from wine and cider. It has been suggested with some plausibility that anaerobic bacteria played an important part in the formation of coal from vegetable substances.

The ripening of ensilage in silos is a process of fermentation caused by bacteria.

In northern Siberia the bodies of the extinct species of elephant called mammoths have been found imbedded in frozen soil where they appear to have lain for thousands of years. In this case the growth of putrefactive bacteria has been prevented by cold, as in the modern refrigerator or cold-storage plant.

The study of bacteria has led to the understanding of many hitherto unexplained phenomena. ‘The unaccountable development of a moist, brilliant red deposit on bread and other articles of food, which was formerly believed by the superstitious to be blood, deposited by some miraculous agency, we know to be due to the growth of a common organism (bacillus prodigiosus). The emission of light by decaying substances when seen in the dark is caused by bacteria as well as other organisms.

It seemed that in some cases in which death has been attributed to the suction of air into the veins, because air appeared to be present inside the heart, the air was in reality a gas formed by certain bacilli that invaded the body just before or just after death (bacillus aérogenes capsulatus).

Woodhead tells us that some savages are in the habit of smearing the soil of certain localities upon their arrows for an arrowpoison, which is intelligible in the light of the fact that soil often contains the bacilli of tetanus (lockjaw).

The comparatively small number of species of bacteria that cause disease are the ones that interest us most, and are those which have been most carefully studied. Since the bacteria in common with other fungi are compelled to derive their food from organic matter, it is easy to understand that they should frequently exist as parasites upon living animals and plants. Pear-blight and some other diseases of plants are caused by bacteria. Bees and other insects, frogs, birds, cattle and a great number of animals besides men suffer from diseases produced by bacteria.

When bacteria are placed upon slips of glass they may be studied with the microscope while alive. Some of them when living are motionless; others wriggle vigorously. Some dart about like minnows in a stream, or they make their way slowly across the field of the microscope like a boat that is being sculled from the stern. By proper methods it-can be shown that the movements are effected through one or more fine, hair-like processes called flagella.

Often it is expedient to study bacteria after drying them on

INTRODUCTION. vi slips of glass, when they may be made more conspicuous by giving them an artificial color (staining). Some of the substances’ of which they are composed readily absorb certain dyes. For this purpose the aniline dyes are used, and their employment has been one of the important factors in making progress in bacteriology possible.

With the microscope alone it is not usually practicable to distinguish accurately between various kinds of bacteria. Micrococci, for instance, which are, in reality, entirely different species, may look very much alike. But differences usually become apparent when the bacteria are grown artificially. The cultivation is done for the most part in test-tubes containing some material which furnishes suitable food. The nutrient materials most used are meat-extract and peptone, which, dissolved with salt in water, constitute nutrient bouillon. Ordinary gelatin, or a vegetable gelatin called agar-agar, may be added to the bouillon when a solid culture-medium is desired. Before these substances can be used for the cultivation of bacteria all other bacteria which they may contain must be de- ot eh eae stroyed by heat. tube containing

Finally, the effects of bacteria in bringing calbire medium: about disease may be tested on the lower animals. The proof that a particular species of bacteria causes a particular disease cannot be considered complete unless the disease can be reproduced by introducing these bacteria into some animal.

Bacteriological Literature.—The student who wishes to pursue bacteriological study in any direction farther than it is possible for the limits of a short manual to go, may, besides consulting the large text-books and weekly medical journals, obtain much assistance from technical periodicals. The Journal of Experimental Medicine, Journal of Medical Research, and the Journal of Infectious Diseases, published in this country, and the English Journal of Pathology and Bacteriology and Journal of Hygiene devote much valuable space to the subject. ;

The Journal of Tropical Medicine also contains contributions. .

A reading knowledge of German and French is very desirable. The Centralblatt fiir Bakteriologie, etc., a German periodical, and the Bulletin de l'Institut Pasteur, published semimonthly in Paris, contain abstracts of most of the important researches made in all parts of the world. The Annales de l'Institut Pasteur, the Zeitschrift fiir Hygiene, the Archiv fiir Hygiene and the Hygienische Rundschau contain many original articles on bacteriological subjects.

The whole literature of any specified subject in bacteriology can be most conveniently found in Baumgarten’s Jahresbericht der Mikroorganismenlehre.

Those who are interested in agricultural bacteriology should read the experiment station records and the various bulletins issued by the Department of Agriculture of the United States. They can usually be obtained upon application to the Department at Washington, D. C. The bacteria that produce disease in domestic animals are described in Dr. V. A. Moore’s book, ‘“‘The Infectious Diseases of Animals,’ Taylor & Carpenter, Ithaca, N. Y., 1906, and in the “Special Report on the Diseases of Cattle,’ United States Department of Agriculture, 1904; also Diseases of the Horse, Department of Agriculture, 1907

Historical Sketch.—Nearly all that we know of bacteria and the part they play in producing disease has been learned during the last half of the last century. Nevertheless, many facts were known long ago, and even by the ancients, which were effective in directing the thought of later years. The epidemic nature of certain maladies was naturally among the earliest of these to be noticed, and was, even until comparatively recent times, attributed to the influence of gods, demons or other supernatural agencies. The superstitions and crude beliefs of the past gave rise to a mass of grotesque theories and fanciful speculations. But with all this we hear of certain beliefs and practices which plainly foreshadowed those of the present day. Latin writers nearly two thousand years ago recorded a relation between insects and malaria which has but lately been proved and explained. The isolation of lepers by the ancient Hebrews shows that the infectious character of the disease has long been recognized, though other affections than leprosy were probably confused with this disease by the ancients. ‘‘He is unclean: he shall dwell alone; without the camp shall his habitation be” (Lev. XIII., 46). There is, in fact, much in the laws of Moses that points to some knowledge of the nature of infections. ‘This is the law, when a man dieth in a tent: all that come into the tent and all that is in the tent shall be unclean for seven days. And every open vessel which has no covering upon it shall be unclean” (Numb. XIX., 14, 15).

“Everything that may abide the fire, ye shall make it go through the fire, and it shall be clean’ (Numb. XXXI., 23).

In Homer we read of Ulysses, that, having slain his wife’s troublesome suitors:

“With fire and sulphur, cure of noxious fumes, He purged the walls and blood-polluted rooms” (Pope’s Odyssey).

*

The massive aqueducts of the Romans still remain to testify that they understood the importance of a pure water-supply.

In Rome there were also sewers for the disposal of drainage, while the Cretans and Assyrians used sewerage systems hundreds and even thousands of years before.

About the fourteenth century we find quarantine against infectious diseases, plague in particular, practiced by certain Italian cities; and the word “quarantine” came into use from

Io MANUAL OF BACTERIOLOGY.

the fact that the period of detention was about forty days (Ital. quarantina) .*

Leeuwenhoek, a citizen of Delft, in Holland (1632-1723) appears to have been the first who actually saw bacteria. Yeast-cells he certainly observed, besides making many other contributions of great value to biology. Leeuwenhoek produced admirable lenses of high magnifying power, and described what he witnessed with singular accuracy and enthusiasm.

Even before this time men had sought to explain the phenomena of infectious diseases by supposing the body to have been penetrated by minute parasites—for example, worms. The spread of such diseases through a community from a single center could readily be accounted for by the multiplication of a contagious element, itself alive (contagium vivum). With increasing knowledge of the abundance of microscopic life these speculations took firmer hold. But long before their truth was finally demonstrated great advances were made in the prevention of infectious diseases. Much honor is due the clinicians, whose accurate observations and foresight accomplished important results at an early day, working with what now seems a very meagre knowledge of the facts.

The production of immunity from small-pox by inoculation was first practiced in oriental countries. The method had long been in use in the East, when in 1718 it was brought to the notice of Europeans by Lady Montagu, wife of the English ambassador at Constantinople. The procedure consisted simply of the introduction of the virus of small-pox by puncture of the skin. An attack of small-pox resulted, which was usually much milder and far less dangerous than the natural disease.

Lady Montagu stated in a letter: “Every year thousands

*J. M. Eager. The Early History of Quarantine. Yellow Fever Institute Bulletin, No. 12. U.S. Marine Hospital Service.

INTRODUCTION. II undergo the operation; and the French ambassador says pleasantly that they take the small-pox here by way of diversion, as they take the waters in other countries.” The mild attacks that followed inoculation were, however, just as contagious to other persons as the natural disease, so that the dangers of this practice to the community were very great.

This was previous to the introducion of vaccination by Edward Jenner in 1796. At this time a belief was current among farmers that a mild form of disease, called cow-pox, acquired by milkers, furnished protection against small-pox, and on investigation Jenner found this belief to be justified. In a few years the practice of vaccination spread to all parts of the world.*