Mycology of the mouth : a text-book of oral bacteria

Front matter

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Sas Gaaastecnteceres

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Contents

INTRODUCTION.—CLASSIFICATION.— MORPHOLOGY ..

BIOLOGY

STERILIZATION

Appendix

Bacillus “ B.” (Vignal) Bacillus ‘ F’.” (Vignal) V. Finkler-Prior Micrococcus Roseus

PAGE

LIST OF ILLUSTRATIONS.

FIG,

PAGE 1.—Morphological forms of bacteria ee ae 5 2.—Types of spore formation. Types of spore peerination Types of flagellation ... ; or i So sos 9) KW) 3.— Involution forms of Breton — ae ak ce ith 4.—Hot air sterilizer ... re i ane a Sea teal 5.—Copper box for sterilizing petri dishes a baie hoe 2atl 6.— Petri dish a a Bes i: ae eo a 7.—Glass capsule io ae sel =e me eee 2 8.—Koch’s steam sterilizer oh oe oe So oS 9.—Autoclave is nee oe owe 4 10.—Koch’s blood serum aati ted ae re) 11.—Unglazed porcelain filters (Pasteur Chamberland) oe OO 12.—Coverglass jar “i oe ee Seb bn ... 40 13.—Hanging drop slide : in “ae ae ed! 14.—Stand to hold bottles of SpE te ae ae w. 45 15.—Boston’s coverslip forceps ... as tae Py: eS 16.—Cornet’s coverslip forceps .. Bes ae ne co) 17.—Bacillus typhi abdominalis, Shouting femal axe aoe OU 18.—Apparatus for filling tubes with nutrient solutions = sop | 19.—Erlenmeyer flask ... es ar ee Fok a eoS 20.—Hot water funnel ... eee te ay fo cso OD) 21.—Potato cutter ae na oe a ae Ae Saye 22.—Roux’s potato tube ee ae AF ee) ve 23.—Platino-iridium inoculating wires... Ah ee sean) GO 24.— Method of inoculating tubes te es - OU) 25.—Hearson’s biological incubator oe ee ve ate Wat 26.— Hearson’s gas valve 382 a ee ee Oo 27.—Buchner’s tube for anierobic plutons oe e .. 64 28.— Bullock’s aniierobic apparatus a: ae ae Soe dade 29.— Wolff bottle oe 65 30.—Filter flask with Pasteur- Coenen filter rena ek Ai eratans toxine oe As oR oe OS

31.—Widal Blood Pipette ees via in ae ». 46 xl1v. List of Illustrations

FIG,

32.—Streptococcus pyogenes in blood. x 1000 ..: -

33.—Streptococeus pyogenes, twenty-four hours’ agar patie x 1000

34.—Streptococcus pyogenes, twenty-four hours’ agar cultivation

35.—Streptococcus pyogenes, agar culture. x 1000 coe

36.—Streptococcus brevis on epithelial cell direct from mouth. x 1000

37.—Streptococcus brevis, twenty-four hours’ agar culture. x 1000

38.—Pipette for collecting pus

39.—Diphtheria bacillus. x 1000 Gram, caine Hour noes old agar

40.—Diphtheria bacillus, forty-eight hours’ old blood serum. Gram. x 1000 ee a e rey

41.—Bacillus diphtheria cultiv Pons (Curtis’ ‘‘ Essentials of Practical Bacteriology ”) ee ay eo is ae

42.—Bacillus tuberculosis, glycerine agar cultivation (Curtis’ ‘* Essentials of Practical Bacteriology”)... : : sre

43.—Bacillus Friedlander gelatin stab (Curtis’ eTieson iets of Practical Bacteriology ’’) ne Se Bo me

44.—Bacillus pyocyaneus, twenty-four hours’ agar cultivation. x 1000 : es. ”

45.—Streptothrix actinomyces Euleoetion on glycerine agar (Carte ‘“‘ Hssentials of Practical Bacteriology’) .

46.—Dental caries affecting enamel

47.—Dental caries affecting dentine

48.—Streptococcus brevis, agar culture at twenty- Sen: Hone x LOOV

49.—Streptococcus brevis, broth culture twenty-four hours. x 1000

50.—Bacillus mesentericus mee twenty-four hours’ agar culture. x 1000

51.—Bacillus subtilis showing spore Pormerion

52.—Bacillus necrodentalis, forty-eight hours’ agar. x 1000 53. xp LOO Fee 54.—Bacillus plexiformis, twenty-four hours, decalcified dentine.

x 1000 55.—Yeasts, from Hyre’s “ [Shafts tiabyatel Teenie 56.—Various forms of mouth bacteria sae 57.—Leptothrix racemosa, balsam mount (Dr. Teor ayant x 1000 58.—Leptothrix racemosa, glycerine mount (Dr. Leon Williams). x 1000 she ae - 59. Sra racemosa, ‘ fruitful Wend: ’ (Dr. Leon Williams). x 2000 a 60.—Leptothrix racemosa, ape direcn x x 1000 ie 61.—Bacillus buccalis maximus, twenty-four hours’ agar. x 1000 62.—Spirillum sputugenum (spirilla forms), mouth direct. x 1000 63.—Spirillum sputugenum (comma forms), mouth direct. x 1000.. 64.—Spirillum sputugenum freshly isolated, twenty-four hours’ agar. x 1000

PAGE

List of Illustrations

FIG.

65.—Spirillum sputugenum (comma Sa twenty-four hours’ agar. x 1000 ae

66.—Spirillum sputugenum Commis Porerie seven ane peor x 1000 67.—Streptothrix buccalis, mouth direct. x 1000 ' 68.—Streptothrix buccalis, forty-eight hours’ agar culture. x 600 69.—Streptothrix buccalis, seven days’ potato culture. x 1000 70.—Streptothrix buccalis, five days’ agar culture ...

71.—Bacillus coli commune, twenty-four hours’ agar. x 1000 72.—Vibrio Finkler-Prior, twenty-four hours’ broth. x 1000

73. —Compound iecicnelatie ll microscope (Watson’s)

74.—Fine adjustment of microscope (Watson’s)

75.—Characters of gelatin stab cultivations (Eyre, after Chester) 76.—Characters of gelatin stab cultivations (Hyre, after Chester) 77.—Types of colonies (Eyre, after Chester)

78.—Types of colonies (Eyre, after Chester)

79.—Detailed character of surface of stab cultures (Eyre, ipa Chester) 80.—Structure of colonies (Eyre, after Chester)

81.--Structure of colonies (Eyre, after Chester)

82.—Fdge of colonies (Eyre, after Chester)

XV.

PAGE

THE MYCOLOGY OF THE MOUTH.

(EASE) Eee le

BacTERIA are minute unicellular organisms forming the lowest group of the Cryptogams, or flowerless plants, and are the intermediate link between the animal and vegetable kingdom of living things, related on the one hand to the Mycetozoa, or animal fungi, on the other to the Algew. They are divisible into two groups, a higher and a lower. The lower, known as Schizomycetes, or fission-fungi, are most numerous, comprising the greater number of the organisms with which pathological mycology deals. They are all microscopic in size, and are rarely more than 5,45, in. in one direction. To facilitate general description mycologists have adopted a standard of measurement designated micron = +-4,, part of millimetre, OY ss355 part of inch, which is written yu, the dimensions of an organism being expressed as multiples or fractions, e.g., 2°5 1 long, 0-75 « wide.” The lower group of bacteria consists of the relatively monomorphous varieties, which are classified according to their shape: (a) small globular bodies, occurring singly or associated with others, designated cocci; (b) rod-shaped forms known as bacilli; (c) spiral or corkscrew forms, and the curved fragments of the same, called spirilla. The term bacteriwm is properly applied to micro-organisms of the schizomycetal group generally, and is used as such in the present work. The higher bacteria are relatively pleomorphous, and may exhibit real or pseudo-branching as in Cladothrix dichotoma ; their method of reproduction as well as their form is allied to the moulds, whilst some of the stages in their life cycle are i)

De THE MYCOLOGY OF THE MOUTH indistinguishable morphologically from the lower group of fission-fungi.

The bacteria as a group are most active chemical agents, splitting up effete animal and vegetable matter into bodies assimilable by plants, fixing free nitrogen as on the roots of Leguminose, and assisting in the disintegration of the hardest rocks. A limited number produce disease in both animals and plants, and finally van Tieghem claims to have demonstrated the presence of the bodies of bacteria in coal, where their activity was concerned in the rotting of the old coal forests.

Classification.—Bacteria belong to the vegetable kingdom, and are placed under the sub-group of Thallophytes, one of the divisions of the Cryptogams, thus :—

I. Thallophytes. — Simple plants, without leaves, stems, roots (ay Tia a PLO. of alley

roots and vascular bundles.

III. Pteridophyta.—Vascular cryp- /( togams, with leaves, stems, true roots, and vascular bundles.

( II. Bryophyta.—Mosses,with leaves

The fungi may be divided into two main groups according to their mode of growth.

eeevarel Schizomycetes .. Fission-fungi. 6 Eumycetes .. .. Higher fungi, generally branching.

The above scheme gives the general position of the bacteria, but it is extremely difficult to properly classify all the organisms generally included in the term ‘‘ bacteria’ ; more particularly is this the case with those species—of which Actinomyces may be taken as an example—which are related to the true Schizomycetes on the one hand and to the EKumycetes on the other.

Most of the forms with which bacteriology has to do belong however to the Schizomycetes, and it is necessary for convenience of description to adopt a classification.

The grouping generally adopted is Baumgarten’s, a modification of that first suggested by Cohn, based upon morphological form, and although not entirely scientific is at present the most convenient.

BACTERIA 3

Baumgarten’s classification is as follows :—

I.—Cocci. ) IT. --Bacilli. Species relatively monomorphous. III.—Spirilla.

I.—Spirulina (Hueppe),.

II.—Leptotrichez (Zoph). Species relatively pleomorphous.

III.—Cladotricheee (Cohn).

IV.—Streptothrix.

Various other methods of classification have been suggested by different observers; thus Du Bary and Hueppe adopt a classification based on spore formation: (1) those bacteria forming endogenous spores ; (2) those forming exogenous or arthrospores. Our knowledge of sporulation is as yet too imperfect to adopt such as a method of classification.

Another source of confusion is the different meaning which authors attach to their terminology; for instance, bacterium is used as a general term including bacteria generally; Hueppe uses it in the limited sense of those organisms which do not produce endogenous spores, the term bacilli being applied to the spore-forming species. Migula calls motile organisms bacilli, non-motile ones bacteria. I have adopted the commonly accepted meaning of bacillus as a rod-shaped organism, and the term bacterium or bacteria as a general one.

Considerable confusion also exists regarding the loosely applied term lepto. thrix, some meaning thereby a thread or special morphological form which is common to a considerable number of species. Zoph, who first used the term, applied it to a distinct species of the higher bacteria, and it is in this sense it is used in the following pages.

Chester (‘‘ Determinative Bacteriology ”) suggests the following classification :-—

CoccacEm.

I.—Cells unbranched, or showing only false branching as in Cladothrix,

(a) Cells globular, becoming slightly elongated before division, which takes place in one, two, or three dimensions.

BACTERIACE, (6) Cells short or long, cylindrical, straight, curved or spiral, without sheath ; motile or non-motile; endospores present or absent. CHLAMYDOBACTERIACAS, (c) Cells surrounded by a sheath and arranged in elongated filaments,

BEGGIATOACEA, (d) Cells not surrounded by a sheath, arranged in filaments and motile by means of an undulating membrane, MYcOBACTERIACEZ.

II. Cells short or long, cylindrical or filaments, clavate, cuneate, or irregular in form. Without endospores, but with formation of gonidia-like bodies by segmentation of the cells. Without flagella. Division at right angles to the rod or filament. Not possessed of sheath, but having true dichotomous branching.

For grouping of species see Chester (‘‘ Determinative Bacteriology,” p. 54). Lehmann and Neumann suggest the following arrangement :—

(1) Coccacee. (2) Bacteriacee. (3) Spirillacee. (4) Corynebacterium, Diphtheria bacillus. (5) Mycobacterium, acid fast organisms (tubercle bacillus). (6) Actinomyces.

Cladothrix, Crenothrix, and Leptothrix are classed as ‘‘ Higher fission-fungi.”’

In both these classifications the genus Bacteriacez are divided into two classes :— (a2) Bacterium—not forming endospores. (b) Bacilli—forming endospores.

For further information see Lehmann and Neumann (p. 119 et seq.), where proper principles for nomenclature of bacteria are laid down.

The Lower Bacteria.— (a) Cocc1—round, oval, or elliptical cells ranging from 0:5 to 2 w in diameter. When not spherical the greatest diameter is not greater than twice the lesser. They are not possessed of motility but often exhibit considerable Brownian movement (p. 11) with the exception of a few species (¢.g., Micrococcus agilis of Cohn, Malta fever coccus). Reproduction is by binary fission, and spore formation (endogenous) is unknown. In some cocci, particularly the streptococci, large swollen elements with increased refractive power are often to be seen; these have been described by Du Bary as a mode of sporulation under the term arthrospores (fig. 1, d.)

The cocci are arranged into groups according to their mode of reproduction.

(1) Srreprococct.—Division (binary fission) occurring regularly in one plane only, the individual elements remain attached by their capsules in the form of chains; in some species the chains may attain great length and be composed of a large number of individual coccl.

(2) SrapHyLococci.—Division occurring irregularly in one plane only, the cocci remaining attached by their capsules in irregular clumps and masses, compared to bunches of grapes.

The number of species in these two groups is very large. The formation of arthrospores is well marked (Du Bary).

(3) Drenococc1.—Division in one plane regularly, the cocci

BACTERIA remaining associated in pairs; both of the foregoing groups exhibit this form, the term being applied to a given species when it occurs

5 most commonly in the diplococcal form (Diplococcus pheumoniee). e ° «@ Oe, ry @ = te 9g” te -oae th @,9 5° Cc 0° fee @ 2° ,° gee’ e, 7 a?

“e, ~ ®%e ®0 ne’ e ® 22 e os ss ORR CA gS os aan

Fic. 1.—MorpxopocicaL Forms oF BACTERIA, a, Cocci ; b, diplococci, diplococcus with capsule ; c, staphylococci; d, streptococci; e, tetracoccus and sarcine; f, various types of bacilli: g, streptobacilli ; h,'spirillum, comma forms and spirochete ; i, streptothrix branched threads, as Micrococcus tetragenous.

(4) Mrrismopepia.—Division in two directions in the same plane, the cocci remaining attached in groups of four, or “ tetrads,”

(5) Sancinz.—Division in three planes, one at right angles to the other two, the cocci remaining attached in cubical packets of eight, which are often associated in masses. These cocci are generally of larger size than the other groups.

The term micrococcus is applied to all the above species, and is also used to designate cocci occurring separately, as mono-coccl ; such mono-coccal form is common among the staphylococct.

(b) Bacruu1.—Rod-shaped organisms, the greatest diameter being more than twice the lesser; the cells may be long or short, but, as a rule, are not wider than 1:0 «. Division generally takes place at right angles to the long axis. The cells of some species have flagella and are motile. Two bacilli may remain united by their capsule, forming a diplobacillus, or the individual elements remaining united in chains a streptobacillus is formed. These two morphological forms are not go constant as the corresponding cocci, and are of little use in classification. Bacilli frequently grow out into long threads, particularly in fluids, to which form the term “‘ leptothrix ”’ is often wrongly applied. Endogenous spore formation occurs in many species. The spores may be central or terminal in position ; round, oval or fusiform in shape. In the latter case the organism containing the spore becomes swollen and spindle-shaped and is termed a Clostridium.

(c) Sprrinta.—Curved or comma-shaped rods and spiral filaments. Reproduction by binary fission or simple division. Generally motile, movement in direction of long axis and rotation upon same axis. In the long spiral threads, also termed spirochete, the motility does not always appear to be due to the presence of flagella, the organisms possessing contractility. The comma-shaped cells generally possess flagella, which may be single or multiple and situated at one or both poles.

The term “ vibrio” is often applied as a generic term to this group; some authors however use ‘‘ vibrio”’ ina special sense, thus Hueppe calls forms without endospores ‘‘ spirochete,” “ vibrio” those having endospores. Migulaapplies the term vibrio to those organisms with only one or two polar flagella, spirilla those with bunches of flagella, and spirochete those without flagella. Fliigge employs ‘‘vibrio”’ to denote forms with but slightly marked undulations.

The Higher Bacteria.—These organisms show a distinct advance on the lower group, but at present our knowledge of them is fragmentary and includes only isolated species. Some of the species show differentiation of the two extremities; one end

BACTERIA ff may be specialised for attachment, the other for reproduction—a method approaching the sporulation of the Moulds, to which the High Bacteria are somewhat closely related. The filaments of these bacteria are generally segmented, but special methods are required to bring out the divisions. There is often a capsule common to the whole thread.

Spirulina (Hueppe).—The cells are sometimes rod-shaped, sometimes spiral, and in some media may grow out into long spiral, undulatory or straight filaments. The threads break up into cocci-like reproductive bodies—‘‘ arthrospores.”” Under this head the Proteus group was first described; they are now generally placed with the bacilli.

Leptothrix (Zoph).—Rod-shaped, spherical and filamentous forms, the last showing a difference between base and apex. Filaments straight or spiral. Spore formation unknown.

This definition of leptothrix is the one I have adopted in the following pages, bacilli forming filaments or threads are not included in it. (See later.)

Cladothrix.—Spherical, rod-shaped, and filamentous forms, the latter show pseudo branching. Reproduction by arthrospores.

Streptothrix.—Felted mycelium-like filaments, showing true dichotomous branching. Club-shaped thickenings appear at the ends of some of the threads. Various forms are produced by breaking up of threads simulating cocci, bacilli and spirilla; from these new individuals may be formed.

Bacteria are also classified according to the environment necessary to their development, as Saprophytes and Parasites.

The saprophytes are those whose existence is possible apart from a living host, and which, obtain the nutriment necessary for their growth from dead organic matter, or from simple organic salts and water.

The strict or obligatory parasites are unable to exist apart from a living host, in whose tissues they multiply, often producing profound pathological changes; some few species may exist in the tissues of an animal without any harm arising.

Such bacteria as are capable of leading a saprophytic existence, but when gaining access to the tissues of the body will develop there, are termed facultative parasites.

Of the obligatory parasites the leprosy bacillus affords a good example; all attempts at its culture have failed, and it is unknown apart from the disease with which its name is associated. The cholera spirillum, typhoid bacillus, and most pathogenic bacteria are examples of the facultative parasite, which, besides the production of disease by development in living animal tissues, is enabled to exist outside the body as a saprophyte.

There are many transitional forms between the obligatory parasite and the saprophytic bacteria; many of these have only been obtained in pure culture within recent years, as, for instance, the influenza bacillus and the gonococeus. An organism living a parasitic existence as a general rule does not grow in artificial media as well as one which has for some time led a purely saprophytic existence. For this reason many bacteria require some little time before they develop their “laboratory habit.” It seems not improbable that the various pathogenic bacteria which are to-day associated with disease were at one time simple saprophytes, and that some of the simple saprophytes, as we know them to-day, may yet attain pathogenic powers.

Not to admit such a development of pathogenic power entails the obscession that pathogenic bacteria were created by design to destroy human life, and, moreover, such a refusal places us at variance with the Monistic conception of the universe, and the orderly operation of the laws of evolution with which all observed phenomena accord.

MorpHoroey has been already referred to as the general basis of classification. Morphological form, however, is extremely variable, so that only the predominating or average form in any given species is taken as representing that species. Thus, for instance, the Pneumococcus or Diplococcus pneumonix occurs generally in the form of diplococci, but also constantly presents a monococcal and streptococcal form. The streptococcus of the mouth occurs in that cavity as a diplococcus almost without exception, whilst in the majority of culture media the streptococcal form predominates. Under certain circumstances the individual cocci may become so much elongated that a form allied to a strepto-bacillus is produced. It is for this reason, as well as for the fact that three chief morphological forms are common to a great number of families, that mycologists have adopted the methods of cultivation in the determination of species.

Chemistry.—The determination of the chemistry of the bacterial cell was first undertaken by Nencki and Schiffer, who found that

BACTERIA 9 the bodies of bacteria were very rich in a nitrogenous substance to which the term micro-protein was applied; with nitric acid this body does not give the xanthoproteic reaction. The percentage of nitrogen is generally about 14:75.

The bacterial bodies also contain some 3°5 per cent. of fat; Bullock has recently extracted a considerable quantity of fat from tubercle bacilli. Bacteria elaborate within their own protoplasm various ferments or enzymes and poisons or toxines; some of these are retained within the bacterial cell and may be obtained from the washed bodies of bacteria by appropriate methods. Thus Buchner obtained an active body, which fermented sugar with the production of alcohol, by expressing the contents of washed and dried yeast. The fermentation produced in no way differed from that brought about by living yeast, the fluid being demonstrably free from living organisms. Quite recently Macfadyen! and Rowland prepared a principle from the washed bodies of typhoid bacilli by triturating them with sterile sand in a special apparatus. The glycerine extract obtained when injected into rabbits induced an agglutinative power in the serum similar to that developed during an attack of typhoid fever in the human subject. Some bacteria give a blue colouration with acidulated iodine, due to the presence of granulose; a number of these are met with in the mouth at various times. The butyric acid-bacilli give this blue reaction with iodine, and are grouped generically as Granulobacteria (Lefar).

Gram’s method of staining (p. 46) also depends on some chemical difference in the composition of the given organism, some retaining the stain, others are quickly decolourised with the alcohol used.

Structure.—The bacterial cell consists of a thin cell wall enclosing clear and, as far as is at present known, structureless contents.

The cell wall, allied but not identical with cellulose, is said to be of a radiate, honeycombed appearance, and that in this layer is situated the colouring matter of the chromogenic organisms, whilst the sulphur granules appearing in the Beggiatoa are contained in the internal plasma.

The plasm also contains at times highly refractile granules which are not spores; these granules are said to be homologous with the chromatin granules of higher plants from the avidity with

' Cent. fir Bak., xxiv., 1902.

which they take up colouring matter—such granules are to be seen in the diphtheria bacillus.

By a delicate process of extraction and subsequent staining with hematoxylin the central plasm of the organism has been shown by Biitschli to be finely reticulated, and that the plasm appears differentiated into a central portion and a parietal layer besides the cell wall; the central mass is therefore a large nucleus, the parietal layer corresponding to the cytoplasm of higher plants.

else a b C Bre. 2.

1, Types of spore-forming bacilli; 2, three types of spore germination ; 3, flagellee: (a) peritrichic, (b) lophotrichic, (c) monotrichic.

Most bacteria are surrounded with a gelatinous, homogeneous covering termed capsule ; in some species—as the pneumococcus of Frankel and the pneumobacilli of Friedlinder—it may be easily demonstrated. It is not always present in cultivations, and is seen best in preparations made from the blood of an animal which has succumbed to infection with the organism. The capsule is also seen in specimens obtained from pneumonic lung and ‘‘ prune juice” sputum.

Many organisms possess the power of independent movement and are described as motile. Upon such organisms extremely

BACTERIA al slender whip-like filaments may be observed by special methods of staining, known as flagella, and may be single and situated at one end, or the organism may be thickly studded with them; they are often many times the length of the organism. Owing to their minute size it is difficult to say to which part of the bacterial cell they are primarily attached. With the exception of a few doubtful species motility is confined to the bacilli and spirilla. By examination of hanging drop preparations the motion can be easily observed, and the organisms seen darting about in all directions. The absence of motility is not always synonymous with absence of flagella, many physical conditions causing ‘ torpidity.”’

Bacteria possessing flagella are classed as (a) Peritrichic, multiple flagella surrounding the bacillus; (b) Lophotrichic, tufts of polar flagella ; (c) Monotrichic, single polar flagella. (Fig. 2.)

re er = ae) Te ko 9

Fic. 3.—INVOLUTION FORMS OF BACTERIA.

Another form of movement which must not be confounded with the above is what is known as ‘‘ Brownian movement,” consisting of a dancing, oscillating swing of the organisms. It is a purely physical condition occurring with solutions of inorganic matter, exactly as with non-motile organisms, and is probably related to surface tension. In determining motility, observe the position of three organisms situated at the angles of an imaginary triangle and watch for a change of relative position, carefully excluding mechanical shock.

Spore Formation.—Various organisms of the class bacilli produce within their plasm highly refractile bodies which are capable of withstanding higher temperatures and stronger disinfectant solutions than the vegetative form ; these bodies are spores.

The spores take up staining reagents with great difficulty, special treatment being necessary (see chapter on microscopical methods). Spore formation consists of a condensation of the cell plasm, the spore thus formed being surrounded with a tough membrane consisting of two layers. At the same time the remainder of the organism undergoes degenerative changes, eventually setting free the mature spore. Certain other clear spaces exist: from time to time in the bacterial plasm, filled with lustrous drops of a fatty nature rendering observation alone useless in the determination of sporulation (page 47).

The number of spores formed by a bacillus is rarely more than one, and is sometimes situated at one end, when the “ drum stick ” form is produced (Tetanus bacillus, fig. 2, 1).

In some species (B. alvei), when the spore is centrally situated the cell plasm alters in form and becomes massed around the spore, forming a clostridium or spindle-shaped mass.

The form and size of the spores differ greatly in various species but is constant for the same species. B. subtilis has ellipsoidal spores 1:2 u length by about 0°6 » breadth.

These spores formed in the interior of bacteria, or endospores as they are termed, are highly resistant to the action of heat, disinfectants, or light, anda proper knowledge of them is of supreme importance in all bacteriological and hygienic work.

Gruber and Brefield found that the spores of B. subtilis required three hours’ boiling at 100° C. to kill them, whereas the rod-shaped forms were easily destroyed by heating for twenty minutes at the temperature of boiling water. When the spore is exposed to favourable conditions it germinates, and in a short time (three to four hours for B. subtilis, Prazmouski) produces the parent form. The process is of three types :—

(1) The spore gradually elongates, the outer membrane disappearing, eventually reaching the adult form which divides by binary fission, in the resulting cells spore formation again taking place.

(2) The spore membrane is ruptured at the point of least resistance, and gradually grows out from the empty spore capsule, which dissolves in the surrounding fluid. The capsule, especially in motile forms, may be seen attached to the free-swimming rod.

(3) Lhe spore membrane ruptures at the equator of the spore, the developing rod gradually forcing its way out by one pole; a portion of the spore may remain attached.

Plasmolysis, or shrinking of the cell plasm with resulting spaces between the plasm and cell wall, may be produced by the action of

BACTERIA ifs certain reagents, among them being the ordinary physiological salt solution (0°75 gm. NaCl in 100 gms. of water). Various staining reagents bring about this phenomenon. The plasmolytic effect may be produced and removed without any apparent injury to the living cell. j

CHAPTER II. The Biology of Bacteria

Bacteria are greatly influenced by their surroundings, and on the other hand often profoundly modify the substratum in which they are growing, be it living tissue or nutrient solution, whilst the very products resulting from their activity are among the chief inhibitory influences restraining their indefinite development.

Cohn estimated that a single bacillus 2 long and 1 uw broad, weighing 0:000000001571 mgrm., and which reproduced itself by binary fission once in half an hour, will in two days’ time have a progeny of 281 billions, occupying a volume of half a litre, while in another three days the mass would be sufficient to fill the beds of all the oceans of the globe, the number of the progeny being represented by 37 places of figures! That such enormous development does not take place is due partly to the antagonism displayed by one species towards another, partly by the insufficiency of nutriment obtainable, but chiefly to the products of the organisms’ own activity. The more important conditions related to the development of bacteria are—light, temperature, gaseous environment, moisture, food supply. The first four factors are related more particularly to the development of the bacteria, whilst the question of food supply is largely complicated by the various chemical changes induced by bacterial action.

Effect of Light.—The antagonism of light to disease was a fact established by empirical observation long before bacteria were known to exist, and the old Italian proverb, ‘‘ Where the sun does not enter, the doctor does,” is illustrative of this popular knowledge gained by observation. Since the discovery of bacteria many experiments have proved the scientific basis of the empirical deduction; the majority of bacteria, and certainly all the known pathogenic forms, are particularly sensitive to the action of light.

Direct sunlight is the most powerful agent; exposure to the

THE BIOLOGY OF BACTERIA ths} direct rays of the sun will kill tubercle bacilli in half an hour, anthrax spores in an hour. Diffused daylight has a similar, but less energetic effect, the time of exposure being about three times as long. The light from an electric arc has a similar effect to diffused daylight; recently advantage has been taken of the fact in the treatment of lupus.’ Tuberculous sputum and typhoid dejecta may thus be deprived of their respective organisms under natural conditions. Hven when the organisms are not entirely destroyed by the process of insolation their pathogenic powers are greatly attenuated, the subsequent cultivations developing less luxuriantly than before the experiment, and the power of producing poisonous products greatly diminished.

Among the bacteria producing pigment, light has marked effect in altering the power of chromogenesis. Thus if a cultivation of the B. rouge d’Kiel—an organism producing a fine red pigment— be exposed to sunlight for a time insufficient to entirely destroy the organisms, subsequent cultures may be obtained which have lost the power of colour-formation and remain colourless indefinitely. A few non-pathogenic bacteria, such as B. violaceous, which forms a purple pigment, apparently thrive best in the light. The red chromogens are generally more resistant to the action of light than other colour-forming species.