44 I. THE STUDY OF BACTERIA surroundings, and Bacon is not an exception. Those who take | After the fall of Napoleon he was given up to the Austrians, up such an extreme position regarding his merits have known too who allowed him to reside at Linz, on condition of never leaving little of the state of contemporary science, and have limited that town. He published a collection of poems at Pest, 1827 their comparison to the works of the scholastic theologians. (2nd ed. Buda, 1835), and also edited the poetical works of Anyos We never find in Bacon himself any consciousness of originality; and Faludi. He died at Linz on the 12th of May 1845. he is rather a keen and systematic thinker, working in a wellbeaten track, from which his contemporaries were being drawn by theology and metaphysics. BIBLIOGRAPHY.-The best work on Roger Bacon is perhaps that of E. Charles, Roger Bacon, sa vie, ses ouvrages, ses doctrines d'après des textes inédits (1861). Against the somewhat enthusiastic estimate and modern interpretation given in this work, are Schneider in his Roger Bacon, Eine Monographie (Augsburg, 1873); K. Werner, Die Psychol.. des Roger Bacon and Die Kosmologie. des Roger Bacon (Vienna, 1879); S. A. Hirsch, Early English Hebraists (1899); Book of Essays (London, 1905), deals with Bacon as a Hebraist. The new matter contained in the publications of Charles and Brewer was summarized by H. Siebert, Roger Bacon: Inaugural Dissertation (Marburg, 1861). Cf. also J. K. Ingram, On the Opus Majus of Bacon (Dublin, 1858); Cousin, Fragments phil. du moyen age" (reprinted from Journal des savans, 1848); E. Saisset, "Précurseurs et disciples de Descartes," pp. 1-58 (reprinted from Revue de deux mondes, 1861); K. Prantl, Gesch. der Logik, iii. 120-129 (a severe criticism of Bacon's logical doctrines); Held, Roger Bacon's praktische Philosophie (Jena, 1881); Karl Pohl, Das Verhältniss d. Philos. zur Theol. bei Roger Bacon (Neustrelitz, 1893); articles in Westminster Review, lxxxi. I and 512; A. Parrot, Roger Bacon el ses contemporains (1894); E. Fluegel, Roger Bacons Stellung in d. Gesch. d. Philos. (1902); S. Vogi, Die Physik Roger Bacos (1906). For the popular legend see Famous Historie of Fryer Bacon (London, 1615; reproduced in Thoms, Early Prose Romances, iii.); R. Greene's Friar Bacon and Friar Bungay (1587 or 1588), and in publication of the Percy Society, vol. xv. 1844, A Piece of Friar Bacon's Brazen Heade's Prophesie (1604). For Bacon as a classical scholar see J. E. Sandys, Hist. of Class. Schol. (2nd ed., 1906), (R. AD.; X.) BACON (through the O. Fr. bacon, Low Lat. baco, from a Teutonic word cognate with " back," e.g. O. H. Ger. pacho, M. H. Ger. backe, buttock, flitch of bacon), the flesh of the sides and back of the pig, cured by salting, drying, pickling and smoking. BACONTHORPE [BACON, BACO, BACCONIUS], JOHN (d. 1346), known as "the Resolute Doctor," a learned Carmelite monk, was born at Baconthorpe in Norfolk. He seems to have been the grandnephew of Roger Bacon (Brit. Mus. Add. MS. 19. 116). Brought up in the Carmelite monastery of Blakeney, near Walsingham, he studied at Oxford and Paris, where he was known " of the Averroists. Renan, however, says that as Princeps The general advances which have been made of late years in the study of bacteria are clearly brought to mind when we reflect that in the middle of the 19th century these organisms were only known to a few experts and in a few forms as curiosities of the microscope, chiefly interesting for their minuteness and motility. They were then known under the name of “animalculae," and were confounded with all kinds of other small organisms. At that time nothing was known of their life-history, and no one dreamed of their being of importance to man and other living beings, or of their capacity to produce the profound chemical changes with which we are now so familiar. At the cxxxi. present day, however, not only have hundreds of forms or species been described, but our knowledge of their biology has so extended that we have entire laboratories equipped for their study, and large libraries devoted solely to this subject. Furthermore, this branch of science has become so complex that the bacteriological departments of medicine, of agriculture, of sewage, &c., have become more or less separate studies. The schizomycetes or bacteria are minute vegetable organisms devoid of chlorophyll and multiplying by repeated bipartitions. They consist of single cells, which may be spherical, "6 he merely tried to justify Averroism against the charge of hetero-oblong or cylindrical in shape, or of filamentous or Definition. doxy. In 1329 he was chosen twelfth provincial of the English other aggregates of cells. They are characterized by the Carmelites. He appears to have anticipated Wycliffe in advocat- absence of ordinary sexual reproduction and by the absence ing the subordination of the clergy to the king. In 1333 he was of an ordinary nucleus. In the two last-mentioned characters sent for to Rome, where, we are told, he first maintained the and in their manner of division the bacteria resemble Schizopope's authority in cases of divorce; but this opinion he retracted. He died in London in 1346. His chief work, Doctoris resoluti phyceae (Cyanophyceae or blue-green algae), and the two groups of Schizophyceae and Schizomycetes are usually united in the Joannis Bacconis Anglici Carmelitae radiantissimi opus super class Schizophyta, to indicate the generally received view that quattuor sententiarum libris (published 1510), has passed through most of the typical bacteria have been derived from the Cyanoseveral editions. Nearly three centuries later, it was still studied phyceae. Some forms, however, such as "Sarcina," have their at Padua, the last home of Averroism, and Lucilio Vanini speaks algal analogues in Palmellaceae among the green algae, while Thaxter's group of Myxobacteriaceae suggests a relationship with the Myxomycetes. The existence of ciliated micrococci together with the formation of endospores-structures not known in the Cyanophyceae-reminds us of the flagellate Protozoa, c.g. BACSANYI, JANOS (1763-1845), Hungarian poet, was born Monas, Chromulina. Resemblances also exist between the endoat Tapolcza on the 11th of May 1763. In 1785 he published his spores and the spore-formations in the Saccharomycetes, and if first work, a patriotic poem, The Valour of the Magyars. In the Bacillus inflatus, B. ventriculus, &c., really form more than one same year he obtained a situation as clerk in the treasury at spore in the cell, these analogies are strengthened. Schizomycetes Kaschau, and there, in conjunction with other two Hungarian such as Clostridium, Plectridium, &c., where the sporiferous cells patriots, edited the Magyar Museum, which was suppressed by enlarge, bear out the same argument, and we must not forget that the government in 1792. In the following year he was deprived there are extremely minute "yeasts," easily mistaken for Microof his clerkship; and in 1794, haying taken part in the conspiracy cocci, and that yeasts occasionally form only one spore in the cell. of Bishop Martinovich, he was thrown into the state prison of Nor must we overlook the possibility that the endosporethe Spielberg, near Brünn, where he remained for two years. formation in non-motile bacteria more than merely resembles After his release he took a considerable share in the Magyar the development of azygospores in the Conjugatae, and some Minerva, a literary review, and then proceeded to Vienna, where Ulothricaceae, if reduced in size, would resemble them. Meyer he obtained a post in the bank, and married. In 1809 he trans-regards them as chlamydospores, and Klebs as carpospores lated Napoleon's proclamation to the Magyars, and, in con- or possibly chlamydospores similar to the endospores of yeast. sequence of this anti-Austrian act, had to take refuge in Paris. 1 Gr. BakrýρLov, Lat. bacillus, little rod or stick. ་་ " of him with great veneration. See Brucker, Hist. Crit. iii. 865; Stöckl, Phil. d. Millel. ii. 1044 1045; Hauréau, Phil. Scol. ii. 476; K. Prantl, Ges. d. Logik, iii. 318. For information as to his life, not found otherwise and of doubtful accuracy, see J. B. de Lezana's Annales Sacri, iv. 46 44 bacillus BACTERIOLOGY. The minute organisms which are commonly called "bacteria "1 are also known popularly under other designations, e.g. microbes," micro-organisms," "microphytes," "bacilli," "micrococci." All these terms, including the usual one of bacteria, are unsatisfactory; for "bacterium," " and "micrococcus" have narrow technical meanings, and the other terms are too vague to be scientific. The most satisfactory designation is that proposed by Nägeli in 1857, namely "schizomycetes," and it is by this term that they are usually known among botanists; the less exact term, however, is also used and is retained in this article since the science is commonly known as "bacteriology." The first part of this article deals with the general scientific aspects of the subject, while a second part is concerned with the medical aspects. 66 tion in space. Nearly all bacteria, owing to the absence of chlorophyll, are saprophytic or parasitic forms. Most of them are colourless, but The former also looks on the ordinary disjointing bacterial cell | liquid (blood, urine, milk, beer, &c.) containing organic matter, as an cidium, and it must be admitted that since Brefeld's dis- or any solid food-stuff (meat preserves, vegetables, &c.), allowed covery of the frequency of minute oidia and chlamydospores to stand exposed to the air soon swarms with bacteria, Distribu among the fungi, the probability that some so-called bacteria- if moisture is present and the temperature not aband this applies especially to the branching forms accepted by normal. Though they occur all the world over in the some bacteriologists-are merely reduced fungi is increased. air and on the surface of exposed bodies, it is not to be Even the curious one-sided growth of certain species which form supposed that they are by any means equally distributed, and sheaths and stalks-e.g. Bacterium vermiforme, B. pediculatum it is questionable whether the bacteria suspended in the air --can be matched by Algae such as Oocardium, Hydrurus, and ever exist in such enormous quantifies as was once believed. some Diatoms. It is clear then that the bacteria are very possibly The evidence to hand shows that on heights and in open a heterogeneous group, and in the present state of our knowledge country, especially in the north, there may be few or even no their phylogeny must be considered as very doubtful. Schizomycetes detected in the air, and even in towns their distribution varies greatly; sometimes they appear to exist in minute clouds, as it were, with interspaces devoid of any, but in laboratories and closed spaces where their cultivation has been promoted the air may be considerably laden with them Of course the distribution of bodies so light and small is easily influenced by movements, rain, wind, changes of temperature, &c. As parasites, certain Schizomycetes inhabit and prey upon the organs of man and animals in varying degrees, and the conditions for their growth and distribution are then very complex. Plants appear to be less subject to their attacks-possibly, as has been suggested, because the acid fluids of the higher vegetable organisms are less suited for the development of Schizomycetes; nevertheless some are known to be parasitic on plants. Schizomycetes exist in every part of the alimentary canal of animals, except, perhaps, where acid secretions prevail; these are by no means necessarily harmful, though, by destroying the teeth for instance, certain forms may incidentally be the forerunners of damage which they do not directly cause. Little was known about these extremely minute organisms before 1860. A. van Leeuwenhoek figured bacteria as far back as the 17th century, and O. F. Müller knew several History. important forms in 1773, while Ehrenberg in 1830 had advanced to the commencement of a scientific separation and grouping of them, and in 1838 had proposed at least sixteen species, distributing them into four genera. Our modern more accurate though still fragmentary knowledge of the forms of Schizomycetes, however, dates from F. J. Cohn's brilliant researches, the chief results of which were published at various periods between 1853 and 1872; Cohn's classification of the bacteria, published in 1872 and extended in 1875, has in fact dominated the study of these organisms almost ever since. He proceeded in the main on the assumption that the forms of bacteria as met with and described by him are practically constant, at any rate within limits which are not wide: observing that a minute spherical micrococcus or a rod-like bacillus regularly produced similar micrococci and bacilli respectively, he based his classification on what may be considered the constancy of forms which he called species and genera. As to the constancy of form, however, Cohn maintained certain reservations which have been ignored by some of his followers. The fact that Schizomycetes produce spores appears to have been discovered by Cohn in 1857, though it was expressed dubiously in 1872; these spores had no doubt been observed previously. In 1876, however, Cohn had seen the spores germinate, and Koch, Brefeld, Pratzmowski, van Tieghem, de Bary and others confirmed the discovery in various species. Distribu tion la time. Spirillum undula, Ehrenb. E. P. syncyanea (Ehrenb.), K FIG. 1. Preparations showing various forms of bacteria and the A. Bacillus subtilis, Cohn, and F. Bacillus typhi, Gaffky. Schroeter. marsch. EsL,M.S. undula (Müller), Ehrenb. (All after Migula.) Migula. a few secrete colouring matters other than chlorophyll. In size their cells are commonly about 0.001 mm. (1 micromillimetre or 1 μ) in diameter, and from two to five times that length, but smaller ones and a few larger ones are known. Some of the shapes assumed by the cells are shown in fig. 1. That bacteria have existed from very early periods is clear from their presence in fossils; and although we cannot accept all the conclusions drawn from the imperfect records of the rocks, and may dismiss as absurd the statements that geologically immured forms have been found still living, the researches of Renault and van Tieghem have shown pretty clearly that large numbers of bacteria existed in Carboniferous and Devonian times, and probably earlier. Schizomycetes are ubiquitous as saprophytes in still ponds and ditches, in running streams and rivers, and in the sea, and especially in drains, bogs, refuse heaps, and in the soil, and wherever organic infusions are allowed to stand for a short time. Any M 66 "6 The supposed constancy of forms in Cohn's species and genera received a shock when Lankester in 1873 pointed out that his Bacterium rubescens (since named Beggiatoa roseo-persicina, Zopf) passes through conditions which would have been described by most observers influenced by the current doctrine as so many separate species or even genera," that in fact forms known as Bacterium, Micrococcus, Bacillus, Leptothrix, &c., occur as phases in one life-history. Lister put forth similar ideas about the same time; and Billroth came forward in 1874 with the extravagant view that the various bacteria are only different states of one and the same organism which he called Cocco-bacteria septica. From that time the question of the pleomorphism (mutability of shape) of the bacteria has been hotly discussed; but it is now generally agreed that, while a | 66 certain number of forms may show different types of cell during the various phases of the life-history, yet the majority of forms are uniform, showing one type of cell throughout their lifehistory. The question of species in the bacteria is essentially the same as in other groups of plants; before a form can be placed in a satisfactory classificatory position its whole lifehistory must be studied, so that all the phases may be known. In the meantime, while various observers were building up our knowledge of the morphology of bacteria, others were laying the foundation of what is known of the relations of these organisms to fermentation and disease-that ancient will-o'-the-wisp spontaneous generation" being revived by the way. When Pasteur in 1857 showed that the lactic fermentation depends on the presence of an organism, it was already known from the researches of Schwann (1837) and Helmholtz (1843) that fermentation and putrefaction are intimately connected with the presence of organisms derived from the air, and that the preservation of putrescible substances depends on this principle. In 1862 Pasteur placed it beyond reasonable doubt that the ammoniacal fermentation of urea is due to the action of a minute Schizomycete; in 1864 this was confirmed by van Tieghem, and in 1874 by Cohn, who named the organism Micrococcus urcae. Pasteur and Cohn also pointed out that putrefaction is but a special case of fermentation, and before 1872 the doctrines of Pasteur were established with respect to Schizomycetes. Meanwhile two branches of inquiry had arisen, so to speak, from the above. In the first place, the ancient question of spontaneous generation" received fresh impetus from the difficulty of keeping such minute organisms as bacteria from reaching and developing in organic infusions; and, secondly, the long-suspected analogies between the phenomena of fermentation 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 extent of immunity enjoyed by the latter, &c., are of the greatest interest and importance. These matters, however, and others such as phagocytosis (first described by Metchnikoff in 1884), and the epoch-making discovery of the opsonins of the blood by reproducing itself had been entertained. Such vague notions began to take more definite shape as the ferment theory of Cagniard de la Tour (1828), Schwann (1837) and Pasteur made way, especially in the hands of the last-named savant From about 1870 onwards the "germ theory of disease" has passed into acceptance. P. F. O. Rayer in 1850 and Davaine had observed the bacilli in the blood of animals dead of anthrax (splenic fever), and Pollender discovered them anew in 1855. In 1863, imbued with ideas derived from Pasteur's researches on fermentation, Davaine reinvestigated the matter, and put forth the opinion that the anthrax bacilli caused the splenic fever; this was proved to result from inoculation. Koch in 1876 published his observations on Davaine's bacilli, placed beyond doubt their causal relation to splenic fever, discovered the spores and the saprophytic phase in the life-history of the organism, and cleared up important points in the whole question (figs. 7 and 9). In 1870 Pasteur had proved that a disease of silkworms was due to an organism of the nature of a bacterium; and in 1871 Oertel showed that a Micrococcus already known to exist in diphtheria is intimately concerned in producing that disease. In 1872, therefore, Cohn was already justified in grouping together a number of "pathogenous" Schizomycetes. Thus arose the foundations of the modern "germ theory of disease;" and, in the midst of the wildest conjectures and the worst of logic, a nucleus of facts was won, which has since grown, and is growing daily. Septicaemia, tuberculosis, glanders, fowl-cholera, relapsing fever, and other diseases are now brought definitely within the range of biology, and it is clear that all contagious and infectious diseases are due to the action of bacteria or, in a few cases, to fungi, or to protozoa or other animals. 64 "" In 1862 Pasteur repeated and extended such experiments, Long before any clear ideas as to the relations of Schizomycetes to fermentation and disease were possible, various thinkers at different times had suggested that resemblances existed between the phenomena of certain diseases and those of fermentation, and the idea that a virus or contagium might be something of the nature of a minute organism capable of spreading and Cladothrix dichotoma, for example, which is ordinarily a branched, filamentous, sheathed form, at certain seasons breaks up into a number of separate cells which develop a tuft of cilia and escape from the sheath. Such a behaviour is very similar to the production of zoospores which is so common in many filamentous algae. MORPHOLOGY.-Sizes, Forms, Structure, &c.-The Schizomycetes consist of single cells, or of filamentous or other groups of cells, according as the divisions are completed at once Form and or not. While some unicellular forms are less than structure. Iμ (001 mm.) in diameter, others have cells measuring 4 or 5μ or even 7 or 8μ in thickness, while the length may vary from that of the diameter to many times that measurement. In the filamentous forms the individual cells are often difficult to observe until reagents are applied (e.g. fig. 14), and the length of the rows of cylindrical cells may be many hundred times greater than the breadth. Similarly, the diameters of flat or spheroidal colonies may vary from a few times to many hundred times that of the individual cells, the divisions of which have produced the colony. The shape of the individual cell (fig. 1) varies from that of a minute sphere to that of a straight, curved, or twisted filament or cylinder, which is not necessarily of the same diameter throughout, 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 long axis-and therefore produce aggregates of long cylindrical shape; but in rarer cases iso-diametric cells divide in two or three directions, producing flat, or spheroidal, or irregular colonies, the size of which is practically unlimited. The bacterial Cell-wall. Cell-wall. 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 the cell-wall of the higher plants, it gives usually no reactions of cellulose, nor is chitin present as in the fungi, but it consists of a proteid substance and is apparently a modification of the general protoplasm. In some cases, however, as in B. tuberculosis, analysis of the cell shows a large amount of cellulose. The cell-walls in some forms swell up into a gelatinous mass so that the cell appears to be surrounded in the unstained condition by a clear, transparent space. When the swollen wall is dense and regular in appearance the term "capsule " is applied to the sheath as in Leuconostoc. Secreted pigments (red, yellow, green and blue) are sometimes deposited in the wall, and some of the iron-bacteria have deposits of oxide of iron in the membranes. d mentioned above, and the term chromatin-granules has been structures are in- a b с Ban 3.30 A 6.0 Cellcontents. 12 p.m. b 0 8.30 a 2pm 2pm 40 12 15 40 ( @ 11. a m. a 10 6.30 6.30 B 9.0 FIG. 2. The various phases of germination of spores of Bacillus remosus (Fraenkel), as actually observed in hanging drops under very high powers. A. The spore sown at 11 A.M., as shown at a, had swollen (b) perceptibly by noon, and had germinated by 3.30 P.M., as shown at c: in d at 6 P.M., and e at 8.30 P.M.; the resulting filament is segmenting into bacilli as it elongates, and at midnight (f) consisted of twelve such segments. B, C. Similar series of phases in the order of the small letters in each case, and with the times of observation attached. At f and g occurs the breaking up of the filament into rodlets. D. Germinating spores in various stages, more highly magnified, and showing the different ways of escape of the filament from the spore-membrane. (H. M. W.) The substance of the bacterial cell when suitably prepared and stained shows in the larger forms a mass of homogeneous protoplasm containing irregular spaces, the vacuoles, which enclose a watery fluid. Scattered in the protoplasm are usually one or more deeply-staining granules. The protoplasm itself may be tinged with colouring matter, bright red, yellow, &c., and may occasionally contain substances other than the deeply-staining granules. The occurrence of a starch-like substance which stains deep blue with iodine has been clearly shown in some forms even where the bacterium is growing on a medium containing no starch, as shown by Ward and others. In other forms a substance (probably glycogen or amylo-dextrin) which turns brown with iodine has been observed. Oil and fat drops have also been shown to occur, and in the sulphur-bacteria numerous fine granules of sulphur. The question of the existence of a nucleus in the bacteria is one that has led to much discussion and is a problem of some difficulty. In the majority of forms it has not hitherto been possible to demonstrate a nucleus of the type which is so characteristic of the higher plants. Attention has Nacleus. . C. D, F. FIG. 3.-Types of Zoogloea. (After Zopf.) tions, and can only A. Mixed zoogloea found as a pellicle on the made clearly surface of vegetable infusions, &c.; it visible by special consists of various forms, and contains cocci (a) and rodlets, in series (b and c), &c. be methods of prepar- Cilia. E Egg-shaped mass of zoogloca of Beggiatoa E, H. Colonies of Myconostoc enveloped at one pole (Lophotrichous), e.g. B. syncyaneus (fig. 1, E), or at Vegetative state. explained. FIG.4.-Types of Spore- Leuconostoc mesenter- in G. Vibrio form with spore. (After Prazmowski.) by the breaking up of the parent cells. | K. Germination of the spore of the hay bacillus (B. subtilis)—the axis of growth of the germinal rodlet is at right angles to the long axis of the spore. L. Germination of spore of Clostridium butyricum-the axis of growth coincides with the long axis of the spore. While many forms are fixed to the substratum, others are free, being in this condition either motile or immotile. The chief of these forms are described below. Cocci: spherical or spheroidal cells, which, according to their aggregates in the form of plates, or solid or hollow and irregular occurring in two or three planes instead of only across the long axis branched colonies. This may be due to the successive divisions (Sarcina), or to displacements of the cells after division. tion. By ÷ individual cell, cell-filament or cell-colony, the immediate groups of cells break away from their former connexion as longer 64 One of the most remarkable c, d, e, f, successive stages in the phenomena in the life-history r, a rodlet segmented in four, each development of the spores. of the Schizomysegment containing one ripe "palmella Zoogloeae. cetes is the formation of this zoogloea stage, g', which corresponds to the. condition of the lower Algae. This occurs as a membrane on the surface of the medium, or as irregular clumps or branched masses (sometimes several inches across) submerged in it, and consists of more or less gelatinous matrix enclosing innumerable "cocci," "bacteria," or other elements of the Schizomycete concerned. Formerly regarded as a distinct genus-the natural fate of all the various FIG. 6.-Bacillus megaterium. (After de Bary) a, b, a chain of motile rodlets still growing and dividing (bacilli). a pair of bacilli actively growing and dividing. divided into four segments) a rodlet in this condition (but after treatment with alcoholic iodine solution. spore. g, g, early stages in the germination of the spores (after being dried several days); hi, h, k, I and m, successive stages in the germination of the spore. 1.Brefeld has observed that a bacterium may divide once every half-hour, and its progeny repeat the process in the same time. One bacterium might thus produce in twenty-four hours a number of segments amounting to many millions of millions. |
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