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certain number of forms may show different types of cell during reproducing itself had been entertained. Such vague notions the various phases of the life-history,' yet the majority of forms began to take more definite shape as the ferment theory of are uniform, showing one type of cell throughout their life. Cagniard de la Tour (1828), Schwann (1837) and Pasteur made history. The question of species in the bacteria is essentially way, especially in the hands of the last-named savant From the same as in other groups of plants; before a form can be about 1870 onwards the “ germ theory of disease” has passed placed in a satisfactory classificatory position its whole life into acceptance. P. F. 0. Rayer in 1850 and Davaine had history must be studied, so that all the phases may be known. observed the bacilli in the blood of animals dead of anthrax In the meantime, while various observers were building up our (splenic fever), and Pollender discovered them anew in 1855. knowledge of the morphology of bacteria, others were laying the In 1863, imbued with ideas derived from Pasteur's researches foundation of what is known of the relations of these organisms on fermentation, Davaine reinvestigated the matter, and put to fermentation and disease--that ancient will-o'-the-wisp forth the opinion that the anthrax bacilli caused the splenic

spontaneous generation " being revived by the way. When fever; this was proved to result from inoculation. Koch in Pasteur in 1857 showed that the lactic fermentation depends 1876 published his observations on Davaine's bacilli, placed on the presence of an organism, it was already known from beyond doubt their causal relation to splenic fever, discovered the researches of Schwann (1837) and Helmholtz (1843) that the spores and the saprophytic phase in the life-history of the fermentation and putrefaction are intimately connected with organism, and cleared up important points in the whole question the presence of organisms derived from the air, and that the (figs. 7 and 9). In 1870 Pasteur had proved that a disease of preservation of putrescible substances depends on this principle. silkworms was due to an organism of the nature of a bacterium; In 1862 Pasteur placed it beyond reasonable doubt that the and in 1871 Oertel showed that a Micrococcus already known to ammoniacal fermentation of urea is due to the action of a minute exist in diphtheria is intimately concerned in producing that Schizomycete; in 1864 this was confirmed by van Tieghen, disease. In 1872, therefore, Cohn was already justified in and in 1874 by Cohn, who named the organism Micrococcus grouping together a number of “pathogenous" Schizomycetes, urcae. Pasteur and Cohn also pointed out that putrefaction is Thus arose the foundations of the modern“ germ theory of but a special case of fermentation, and before 1872 the doctrines disease;" and, in the midst of the wildest conjectures and the of Pasteur were established with respect to Schizomycetes. worst of logic, a nucleus of facts was won, which has since Meanwhile two branches of inquiry had arisen, so to speak, grown, and is growing daily. Septicaemia, tuberculosis, glanders, from the above. In the first place, the ancient question of fowl-cholera, relapsing fever, and other diseases are now brought

spontaneous generation " received fresh impetus from the definitely within the range of biology, and it is clear that difficulty of keeping such minute organisms as bacteria from all contagious and infectious diseases are due to the action reaching and developing in organic infusions; and, secondly, of bacteria or, in a few cases, to fungi, or to protozoa or other the long-suspected analogies between the phenomena of fer- animals. mentation and those of certain diseases again made themselves Other questions of the highest importance have arisen from felt, as both became better understood. Needham in 1745 had the foregoing. About 1880 Pasteur first showed that Bacillus declared that heated infusions of organic matter were not

anthracis cultivated in chicken broth, with plenty of oxygen deprived of living beings; Spallanzani (1777) had replied that and at a temperature of 42-43° C., lost its virulence after a few more careful heating and other precautions prevent the appear- "generations," and ceased to kill even the mouse; Toussaint ance of organisms in the fluid. Various experiments by Schwann, and Chauveau confirmed, and others have extended the observaHelmholtz, Schultz, Schroeder, Dusch and others led to the tions. More remarkable still, animals inoculated with such refutation, step by step, of the belief that the more minute attenuated ” bacilli proved to be curiously resistant to the organisms, and particularly bacteria, arose de novo in the special deadly effects of subsequent inoculations of the non-attenuated cases quoted. Nevertheless, instances were adduced where the form. In other words, animals vaccinated with the cultivated most careful heating of yolk of egg, milk, hay-infusions, &c., bacillus showed immunity from disease when reinoculated with had failed, -the boiled infusions, &c., turning putrid and the deadly wild form. The questions as to the causes and swarming with bacteria after a few hours.

nature of the changes in the bacillus and in the host, as to the In 1862 Pasteur repeated and extended such experiments, extent of immunity enjoyed by the latter, &c., are of the greatest and paved the way for a complete explanation of the anomalies; interest and importance. These matters, however, and others Cohn in 1872 published confirmatory results; and it became such as phagocytosis (first described by Metchnikoff in 1884), clear that no putrefaction can take place without bacteria or and the epoch-making discovery of the opsonins of the blood by some other living organism. In the hands of Brefeld, Burdon- Wright, do not here concern us (see II. below). Sanderson, de Bary, Tyndall, Roberts, Lister and others, the MORPHOLOGY.-Sizes, Forms, Structure, &c.—The Schizomyvarious links in the chain of evidence grew stronger and stronger, cetes consist of single cells, or of filamentous or other groups of and every case adduced as one of “

spontaneous generation" cells, according as the divisions are completed at once fell to the ground when examined. No case of so-called " spon

or not. While some unicellular forms are less than taneous generation” has withstood rigid investigation; but the IM (.oqi mm.) in diameter, others have cells measurdiscussion contributed to more exact ideas as to the ubiquity, ing 44 or 54 or even 74 or 8u in thickness, while the length may minuteness, and high powers of resistance to physical agents vary from that of the diameter to many times that measurement. of the spores of Schizomycetes, and led to more exact ideas In the filamentous forms the individual cells are often difficult of antiseptic treatments. Methods were also improved, and

to observe until reagents are applied (e.g. fig. 14), and the length the application of some of them to surgery at the hands of of the rows of cylindrical cells may be many hundred times Lister, Koch and others has yielded results of the highest greater than the breadth. Similarly, the diameters of flat or value.

spheroidal colonies may vary from a few times to many hundred Long before any clear ideas as to the relations of Schizomycetes times that of the individual cells, the divisions of which have to fermentation and disease were possible, various thinkers at produced the colony. The shape of the individual

Cel-wall. different times had suggested that resemblances existed between cell (fig. 1) varies from that of a minute sphere to the phenomena of certain diseases and those of fermentation, that of a straight, curved, or twisted filament or cylinder, and the idea that a virus or contagium might be something of which is not necessarily of the same diameter throughout, and the nature of a minute organism capable of spreading and may have flattened, rounded, or even pointed ends. The rule is

that the cells divide in one direction only-i.e. transverse to the · Cladothrix dichotoma, for example, which is ordinarily a branched, long axis—and therefore produce aggregates of long cylindrical filamentous, sheathed form, at certain seasons breaks up into a number of separate cells which develop a tust of cilia and escape from shape; but in rarer cases iso-diametric cells divide in two or the sheath. Such a behaviour is very similar to the production of three directions, producing flat, or spheroidal, or irregular zoospores which is so common in many filamentous algae.

colonies, the size of which is practically unlimited. The bacterial

Form and structure. Chri






12 pm .

12 15


9 am

cell is always clothed by a definite cell-membrane, as was shown accordingly been directed to the deeply-staining granules by the plasmolysing experiments of Fischer and others. Unlike mentioned above, and the term chromatin-granules has been

the cell-wall of the higher plants, it gives usually no applied to them, and they have been considered to represent

reactions of cellulose, nor is chitin present as in the a rudimentary nucleus. That these granules consist of a material fungi, but it consists of a proteid substance and is apparently similar to the chromatin of the nucleus of higher forms is very a modification of the general protoplasm. In some cases, how- doubtful, and the comparison with the nucleus of more highly ever, as in B. luberculosis, analysis of the cell shows a large organized cells rests on a very slender basis. The most recent amount of cellulose. The cell-walls in some forms swell up into works (Vejdovsky, Mencl), however, appear to show that nuclei a gelatinous mass so that the cell appears to be surrounded in of a structure and mode of division almost typical are to be found the unstained condition by a clear, transparent space. When in some of the largest bacteria. It is possible that a similar the swollen wall is dense and regular in appearance the term structure has been " capsule” is applied to the sheath as in Leuconosloc. Secreted overlooked or is inpigments (red, yellow, green and blue) are sometimes deposited visible in other in the wall, and some of the iron-bacteria have deposits of oxide forms owing to of iron in the membranes.

their small size, and

that there may be 8 c

another type of nuc8

leus—the diffuse

nucleus - such a2pm

Schaudinn believed

to be the case in A


B. butschlii. Many

bacteria when sus-
pended in a fluid

exhibit a power of
12 pm

independent move

ment which is, of
2pm 40

course, quite dis-
tinct from the
Brownian move-
ment-a non-vital

phenomenon com-

mon to all finely-
divided particles

suspended in a fluid.

Independent move-
ment is effected by

special motile or. FIG. 2:--The various phases of germination of spores of Bacillus gans, the cilia or

H ramosus (Fraenkel), as actually observed in hanging drops under flagella. These very high powers.

structures are inA. The spore sown at 11 A.M., as shown at a, had swollen (6) per: visible, with ordinaptibly by noon, and had germinated by 3:30 P.M., as shown at c: indary illumination in at 6 P... and e' at 8.30 P.M.; the resulting filament is segmenting living cells or uninto bacilli as it elongates, and at midnight ) consisted of twelve

stained prepara. Fig. 3.—Types of Zoogloea. (Aster Zopf.) B, C. Similar series of phases in the order of the small letters tions, and can only A. Mixed zoogloea found as a pellicle on the in each case, and with the times of observation attached. At f and be made clearly

surface of vegetable infusions, &c.; it & occurs the breaking up of the filament into rodlets.

consists of various forms, and contains D. Germinating spores in various stages, more highly magnified,

visible by special

cocci (a) and rodlets, in series (b and c). and showing the different ways of escape of the filament from the methods of prepar- &c. spore-membrane. (H. M. W.)

ation and staining B. Egg-shaped mass of zoogloea of Beggialog

first used by Löffler. roseo-persicina (Bacterium rubescens of The substance of the bacterial cell when suitably prepared By these methods

Lankester); the gelatinous swollen walls and stained shows in the larger forms a mass of homogeneous the cilia are seen to

of the large crowded cocci are fused into

a common gelatinous envelope. protoplasm containing irregular spaces, the vacuoles, be fine protoplasmic C. Reticulate zoogloea of the same. catents. which enclose a watery fluid. Scattered in the proto- outgrowths of the D, E, H. Colonies of Myconostoc enveloped

plasm are usually one or more deeply-staining granules. cell (fig. 1) of the F. Branched fruticose zoogsoea of Cladothrix The protoplasm itself may be tinged with colouring matter, same nature as those

(slightly magnified). bright red, yellow, &c., and may occasionally contain substances of the zoospores and G. Zoogloea of Bacterium merismopedioides, other than the deeply-staining granules. The occurrence of a antherozoids of Zops, containing cocci arranged in tablets. starch-like substance which stains deep blue with iodine has algae, mosses, &c. been clearly shown in some forms even where the bacterium These cilia appear to be attached to the cell-wall, being unaffected is growing on a medium containing no starch, as shown by by plasmolysis, but Fischer states that they really are derived from Ward and others. In other forms a substance (probably the central protoplasm and pass through minute pores in glycogen or amylo-dextrin) which turns brown with iodine the wall. The cilia may be present during a short period has been observed. Oil and fat drops have also been shown only in the life of a Schizomycete, and their number may vary to occur, and in the sulphur-bacteria numerous fine granules according to the medium on which the organism is growing.

Nevertheless, there is more or less constancy in the type of distriThe question of the existence of a nucleus in the bacteria is bution, &c., of the cilia for each species when growing at its best. one that has led to much discussion and is a problem of some The chief results may be summed up as follows: some species,

difficulty. In the majority of forms it has not hitherto e.g. B. anthracis, have no cilia; others have only one flagellum

been possible to demonstrate a nucleus of the type at one pole (Monotrichous), e.g. Bacillus pyocyaneus (fig. 1, C, D), which is so characteristic of the higher plants. Attention has lor one at each pole; others again have a tuft of several cilia


such segments.

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at one pole (Lopholrichous), c.8. B. syncyaneus (fig. 1, E), or at | aggregates in the form of plates, or solid or hollow and irregular each pole (Amphitrichous) (fig. 1, J, K, L); and, finally, many occurring in two or three planes instead of only across the long axis

branched colonies. This may be due to the successive divisions actively motile forms have the cilia springing all round (Peri- (Sarcina), or to displacements of the cells after division. Irichous), e.g. B. vulgaris (fig. 1, G). It is found, however, that strict reliance cannot be placed on the distinction between individual cell, cell-filament or cell-colony, the immediate

Growth and Division.-Whatever the shape and size of the the Monotrichous, Lophotrichous and Amphitrichous conditions, visible results of active nutrition are elongation of since one and the same specics may have one, two or more cilia the cell and its division into two equal halves,

Reproduc at one or both poles; nevertheless some stress may usually be laid on the existence of one or two as opposed to several-1.8. which either splits at once or remains intact for a shorter or

across the long axis, by the formation of a septum, five or six or more-at one or each pole.

In the In Beggiatoa, a filamentous form, peculiar, slow, oscillatory longer time. This process is then repeated and so on.

first case the separated movements are to be observed, reminding us of the movements

А .B

с cells assume the char- ;

3 of Oscillatoria among the Cyanophyceae. In these Vegetative

acter of the parentcases no cilia have bcen observed, and there is a

cell whose division firm cell-wall, so the movement remains quite un

gave rise to them; in explained.

the second case they
FIG.4.-Types of Spore-
formation in Schizomy.

form filaments, or, if

cetes. (After Zopf.)

the further elongation A. Various stages in the and divisions of the development of the

cells proceed in differendogenous spores in

Fig. 5.-Characteristic groups of MicroClostridium - the

ent directions, plates cocci. (Aster Cohn.) A. Micrococcus prosmall letters indicate or spheroidal or other digiosus. B. M. vaccinge. c. Zoogiaa the order.

shaped colonies. It stage of a Micrococcus, forming a close B. Endogenous spores of

membrane on infusion-Pasteur's Myco. not unfrequently hap- derma. (Very highly magnified.)

C. A chair of cocci of pens, however, that

Leuconostoc mesenter groups of cells break away from their former connexion as longer
ioides, with

or shorter straight or curved filaments, or as solid masses. In resting spores," i.e. some filamentous forms this “ fragmentation "into multicellular arthrospores. (After van Tieghem.)

pieces of equal length or nearly so is a normal phenomenon, D. A motile rodlet with each partial filament repeat

one cilium and with a ing the growth, division and K

spore formed inside.

fragmentation as before (cf. 0

e. Spore formation

Vibrio - like (c) and figs. 2 and 6). By rapid divi-
Spirillum-like (a, b, c) sion hundreds of thousands

Schizomycetes. of cells may be produced in
F. Long rod-likeform con-

a few hours, and, according
taining a spore (these
the so-called

to the species and the con-
" Köpfchenbacterien" ditions (the medium, temper-

of German authors). ature, &c.), enormous colG. Vibrio form with spore. (Aster Prazmowski.)

lections of isolated cells may H. Clostridium-one cell contains two spores. . (Aster Prazmowski? | cloud the fluid in which they 1. Spirillum containing many spores (a), which are liberated at ó by the breaking up of the parent cells.

are cultivated, or form deK. Germination of the spore of the hay bacillus (B. subtilis)—the posits below or films on its

axis of growth of the germinal rodiet is at right angles to the surface; valuable characters

long axis of the spore. L. Germination of spore of Clostridium butyricum—the axis of

are sometimes obtained from

Fig. 6.- Bacillus megaterium.

When growth coincides with the long axis of the spore.

these appearances.

(Aster de Bary) these dense swarms

of While many forms are fixed to the substratum, others are

a, a chain of motile rodlets still

growing and dividing (bacilli). free, being in this condition either motile or immotile. The vegetative cells become fixed chief of these forms are described below.

in a matrix of their own b, a pair of bacilli actively growing swollen contiguous cell-walls,

and dividing; Cocci: spherical or spheroidal cells, which, according to their

p, a rodlet in this condition (but

divided into four segments) relative (not very well defined) sizes are spoken of as Micro they pass over into a sort of cocci, Macrococci, and perhaps Monas forms.

resting state as a so-called after treatment with alcoholic Rods or rodlets: slightly or more considerably elongated cells zoogloca (fig. 3).

iodine solution. which are cylindrical, biscuit-shaped or somewhai susiform. The cylindrical forms are short, i.e. only three or four times phenomena in the life-history », a rodlet segmented in lour, each

One of the most remarkable c, d, e, f, successive stages in the

development of the spores. as long as broad (Bacterium), or longer (Bacillus); the biscuitshaped ones are Bacteria in the early stages of division. of the Schizomy

segment containing one ripe

Clostridia, &c., are spindle-shaped.

cetes is the forma

spore. Filaments really consist of clongated cylindrical cells which remain tion of this zoogloea stage, s', 83scarry stages in the ger. united end to end after division, and they may break up

mination of the spores (after

which corresponds to the. later into clements such as those described above. Such fila.

being dried several days): ments are not always of the same diameter throughout, and

condition of the hi, hi

,, I and m, successive
their segmentation varies considerably. They may be free or lower Algae. This occurs as a stages in the germination of
attached at one (the "basal ") end. A distinction is made membrane on the surface of
between simple filaments (e.g: Leplothrix) and such as exhibit the medium, or as irregular

a false branching (e.g. Cladothrix). Curved and spiral forms. Any of the elongated forms described clumps or branched masses (sometimes severai inches across)

above may be curved or sinuous or twisted into a corkscrew submerged in it, and consists of more or less gelatinous
like spiral instead of straight. If the sinuosity is slight we matrix enclosing innumerable " cocci," " bacteria," or other
have the Vibrio form; if pronounced, and the spiral wind- elements of the Schizomycete concerned. Formerly regarded
ing well marked, the forms are known as Spirillum, Spiro-
chacte, &c. These and similar terms have been applied partly as a distinct genus—the natural fate of all the various
to individual cells, but more often to filaments consisting of 1. Brefeld has observed that a bacterium may divide once every
several cells; and much confusion has arisen from the dish. hall-hour, and its progeny repeat the process in the same time. One
culty of defining the terms themselves.

bacterium might thus produce in twenty-four hours a number of In addition to the above, however, certain Schizomycetes present segments amounting to many millions of millions.

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forms-the zoogloea is now known to be a sort of resting con- | active along the whole length; (a) there are optimum, minimum dition of the Schizomycetes, the various elements being glued and maximum temperatures, other conditions remaining constant, together, as it were, by their enormously swollen and diffluent at which growth begins, runs at its best and is soon exhausted, cell-walls becoming contiguous. The zoogloea is formed by active respectively; (3) that the most rapid cell-division and maximum division of single or of several mother-cells, and the progeny growth do not necessarily accord with the best conditions for appear to go on secreting the cell-wall substance, which then the life of the organism; and (4) that any sudden alteration of absorbs many times its volume of water, and remains as a temperature brings about a check, though a slow rise may consistent matrix, in which the cells come to rest. The matrix accelerate growth (fig. 8). It was also shown that exposure to -ie. the swollen cell-walls-in some cases consists mainly of light, dilution or exhaustion of the food-media, the presence of cellulose, in others chiefly of a proteid substance; the matrix traces of poisons or metabolic products check growth or even in some cases is horny and resistant, in others more like a thick bring it to a standstill; and the death or injury of any single solution of gum. It is intelligible from the mode of formation cell in the filamentous series shows its effect on the curve by that foreign bodies may become entangled in the gelatinous lengthening the doubling period, because its potential progeny · matrix, and compound zoogloeae may arise by the apposition have been put out of play. Hardy has shown that such a of several distinct forms, a common event in macerating troughs destruction of part of the filament may be effected by the attacks (fig. 3, A). Characteristic forms may be assumed by the young of another organism. zoogloea of different species,--spherical, ovoid, reticular, filamentous, fruiticose, lamellar, &c.,-but these vary considerably as the mass increases or comes in contact with others. Older



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FIG. 7.-Bacillus anthracis. (After Koch.)

co A. Bacilli mingled with blood-corpuscles from the blood of a guinea-pig; some of the bacilli dividing.

B. The rodlets after three hours' culture in a drop of aqueous 60 humour. They grow out into long leptothrix-like filaments, which

Temp become septate later, and spores are developed in the segments.

40 zooglocae may precipitate oxide of iron in the matrix, if that metal exists in small quantities in the medium. Under favour- 20 able conditions the elements in the zoogloea again become


lamp dari active, and move out of the matrix, distribute themselves in the surrounding medium, to grow and multiply as before. Il

2 pm. 233 the zoogloea is formed on a solid substratum it may become firm and horny; immersion in water softens it as described (Fraenkei),

constructed from data such as in fig. 4. The abscissae

FIG. 8.-Curve of growth of a filament of Bacillus ramosus above.

represent intervals of time, the ordinates the measured lengths of The growth of an ordinary bacterium consists in uniform the growing filament. Thus, at 2.33 P.M. the length of the filament elongation of the rodlet until its length is doubled, followed was 6 wiat 5:45, 20w; at 8 P.M., 70 m and so on. Such curves show

by division by a median septum, then by the simul- differences of steepness according to the temperature (sec temp: Measure Reat of taneous doubling in length of each daughter cell, again curve), and to alterations of light (lamp) and darkness. (H. M. W.; growth.

followed by the median division, and so on (figs. 13, 14). A very characteristic method of reproduction is that of spore

If the cells remain connected the resulting filament formation, and these minute reproductive bodies, which represent repeats these processes of elongation and subsequent division a resting stage of the organism, are now known in many

Spores. uniformly so long as the conditions are maintained, and very forms. Formerly two kinds of spores were described, accurate measurements have been obtained on such a form, arthrospores and endos pores. An arthrospore, however, is not a eg. B.samosus. Ií a rodlet in a hanging drop of nutricnt gelatine true sporc but merely an ordinary vegetative cell which separates is fixed under the microscope and kept at constant temperature, and passes into a condition of rest, and such may occur in forms a curve of growth can be obtained recording the behaviour which form endospores, e.g. B. subtilis, as well as in species not during many hours or days. The measured lengths are marked known to form endospores. The true spore or endospore begins off on ordinates erected on an abscissa, along which the times with the appearance of a minute granule in the protoplasm of a are noted. The curve obtained on joining the former points vegetative cell; this granule enlarges and in a few hours has then brings out a number of facts, foremost among which are taken to itself all the protoplasm, secreted a thin but very (1) that as long as the conditions remain constant the doubling resistive envelope, and is a ripe ovoid spore, smaller than the periods--i.e. the times taken by any portion of the filament to mother-cell and lying loosely in it (cf. figs. 6, 9, 10, and 11). double its length—are constant, because each cell is equally in the case of the simplest and most minute Schizomycetes


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Fig. 9.

(Micrococcus, &c.) no definite spores have been discovered; any from the year 1872, when Cohn published his system, which was one of the vegetative micrococci may commence a new series extended in 1875; this scheme has in fact dominated

Classificeof cell by growth and division. We may call these forms the study of bacteria ever since. Zopf in 1885 proposed asporous," at any rate provisionally.

a scheme based on the acceptance of extreme views The spore may be formed in short or long segments, the cell- of pleomorphism; his system, however, was extraordinarily wall of which may undergo change of form to accommodate itself to the contents. As a rule only one spore is formed in a

cell, and the process usually takes place in a bacillar segment.
In some cases the spore-forming protoplasm gives a blue reaction
with iodinc solutions. The spores may be developed in cells

which are actively swarming, the move-
ments not being interfered with by the
process (fig. 4, D). The so-called
“Köpfchenbacterien " of older writers are
simply bacterioid segments with a spore
at one end, the mother cell-wall having
adapted itself to the outline of the spore
(fig. 4, F). The ripe spores of Schizomy.
cetes are spherical, ovoid or long-ovoid in
shape and extremely minute (e.g. those of FIG. 10 –Bacillus subtilis. (After Strasburger.) A. Zoogloea
Bacillus subtilis measure o.0012 mm. long pellicle,

B. Motile rodlets,

C. Development of by 0.0006 mm. broad according to Zopf), spores. highly refractive and colourless (or very impracticable and was recognized by him as provisional only. dark, probably owing to the high index of Systems have also been brought forward based on the formation

refraction and minute size). The membrane of arthrospores and endospores, but as explained above this is B

may be relatively thick, and even exhibit eminently unsatisfactory, as arthrospores are not true spores shells or strata.

and both kinds of reproductive bodies are found in one and the The germination of the spores has now same form. Numerous attempts have been made to construct been observed in several forms with care. schemes of classification based on the power of growing colonies The spores are capable of germination at once, or they may be kept for months and even years, and are very resistant against A

9 AM desiccation, heat and cold, &c. In a suitable medium and at a proper temperature

the germination is completed in a few hours. A, Bacillus anthre. The spore swells and elongates and the B

10.40 cis. (Aster de Bary.) contents grow forth to a cell like that which Two of the long fila. produced it, in some cases clearly breaking ments (B, fig. 10), in through the membrane, the remains of being developed. The which may be seen attached to the young specimen was culti, germinal rodlet (figs. 5, 9 and 11); in other с vated in broth, and

12.30 cases the surrounding membrane of the spores are drawn a little small — spore swells and dissolves. The germinal they should be of the cell then grows forth into the forms typical same diameter trans- for the particular Schizomycete concerned. versely as the seg.

The conditions for spore-formation differ.
B. Bacillus sub- Anaerobic species usually require little D

4 P.M. tilis. (Aster de oxygen, but aerobic species a free supply. Bary.) i, fragments Each species has an optimum temperature of filaments with ripe and many are known to require very special sive stages in the food-media. The systematic interference germination of the with these conditions has enabled bacterio

E30 spores, the remains logists to induce the development of so

8 P.M. of the


at: called asporogenous races, in which the tached to the ger- formation of spores is indefinitely postponed, (Fraenkel), in the order and at the times given, in a hanging drop

FIG. 11.-Stages in the development of spores of Bacillus ramosas changes in vigour, virulence and other pro- culture, under a very high power. The process begins with the for.

perties being also involved, in some cases mation of brilliant granules (A, B); these increase, and the brilliant at any rate. The addition of minute traces of acids, poisons, &c., substance gradually balls together (C) and forms the spores (D), one leads to this change in some forms; high temperature has also

in cach segment, which soon acquire a membrane and ripen (E).

(H. M. W.) been used successfully.

The difficult subject of the classification of bacteria dates to liquefy gelatine, to secrete coloured pigments, to ferment

.The difficulties presented by such minute and simple organisms certain media with evolution of carbon dioxide or other gases, as the Schizomycetes are due partly to the few "characters which or to induce pathological conditions in animals. None of these they possess and partly to the dangers of error in manipulating systems, which are chiefly due to the medical bacteriologists, them; it is anything but an easy matter either to trace the whole has maintained its position, owing to the difficulty of applying development ot a single form or to recognize with certainty any the characters and to the fact that such properties are physioone stage in the development unless the others are known. This being the case, and having regard to the minuteness and ubiquity | logical and liable to great fluctuations in culture, because a of these organisms, we should very careful in accepting evidence given organism may vary greatly in such respects accordi to as to the continuity or otherwise of any two forms which falls short its degree of vitality at the time, its age, the mode of nutrition of direct and uninterrupted observation. The outcome of all these considerations is that, while recognizing that the "genera" and observed; or, at any rate, the strictest rules should be followed in species " as defined by Cohn must be recast, we are not warranted accepting the evidence adduced to render the union of any forms in uniting any forms the continuity of which has not been directly I probable.




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