Encyclopaedia Britannica Volume 3, Part 1, Slice 2 Part 1

Encyclopaedia Britannica, 11th Edition.

Volume 3, Part 1, Slice 2.

by Various.

VOLUME III

AUSTRIA LOWER to BISECTRIX

[v.03 p.0156]

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 as "Princeps" of the Averroists. Renan, however, says that he merely tried to justify Averroism against the charge of heterodoxy. In 1329 he was chosen twelfth provincial of the English Carmelites. He appears to have antic.i.p.ated Wycliffe in advocating the subordination of the clergy to the king. In 1333 he was sent for to Rome, where, we are told, he first maintained the pope's authority in cases of divorce; but this opinion he retracted. He died in London in 1346. His chief work, _Doctoris resoluti Joannis Bacconis Anglici Carmelitae radiantissimi opus super quattuor sententiarum libris_ (published 1510), has pa.s.sed through several editions.

Nearly three centuries later, it was still studied at Padua, the last home of Averroism, and Lucilio Vanini speaks of him with great veneration.

See Brucker, _Hist. Crit._ iii. 865; Stockl, _Phil. d. Mittel._ ii.

1044-1045; Haureau, _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.

BACSANYI, JANOS (1763-1845), Hungarian poet, was born at Tapolcza on the 11th of May 1763. In 1785 he published his first work, a patriotic poem, _The Valour of the Magyars_. In the same year he obtained a situation as clerk in the treasury at Kaschau, and there, in conjunction with other two Hungarian patriots, edited the _Magyar Museum_, which was suppressed by the government in 1792. In the following year he was deprived of his clerks.h.i.+p; and in 1794, having taken part in the conspiracy of Bishop Martinovich, he was thrown into the state prison of the Spielberg, near Brunn, where he remained for two years. After his release he took a considerable share in the _Magyar Minerva_, a literary review, and then proceeded to Vienna, where he obtained a post in the bank, and married. In 1809 he translated Napoleon's proclamation to the Magyars, and, in consequence of this anti-Austrian act, had to take refuge in Paris. After the fall of Napoleon he was given up to the Austrians, who allowed him to reside at Linz, on condition of never leaving that town. He published a collection of poems at Pest, 1827 (2nd ed. Buda, 1835), and also edited the poetical works of Anyos and Faludi. He died at Linz on the 12th of May 1845.

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,"

"bacillus" and "micrococcus" have narrow technical meanings, and the other terms are too vague to be scientific. The most satisfactory designation is that proposed by Nageli 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.

I. THE STUDY OF BACTERIA

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 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.

[Sidenote: Definition.]

The schizomycetes or bacteria are minute vegetable organisms devoid of chlorophyll and multiplying by repeated bipart.i.tions. They consist of single cells, which may be spherical, oblong or cylindrical in shape, or of filamentous or other aggregates of cells. They are characterized by the absence of ordinary s.e.xual reproduction and by the absence of an ordinary nucleus. In the two last-mentioned characters and in their manner of division the bacteria resemble Schizophyceae (Cyanophyceae or blue-green algae), and the two groups of Schizophyceae and Schizomycetes are usually united in the cla.s.s Schizophyta, to indicate the generally received view that most of the typical bacteria have been derived from the Cyanophyceae.

Some forms, however, such as "Sarcina," have their algal a.n.a.logues in Palmellaceae among the green algae, while Thaxter's group of Myxobacteriaceae suggests a relations.h.i.+p 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, _e.g._ _Monas_, _Chromulina_. Resemblances also exist between the endospores and the spore-formations in the Saccharomycetes, and if _Bacillus inflatus_, _B. ventriculus_, &c., really form more than one spore in the cell, these a.n.a.logies are strengthened. Schizomycetes such as _Clostridium_, _Plectridium_, &c., where the sporiferous cells enlarge, bear out the same argument, and we must not forget that there are extremely minute "yeasts," easily mistaken for Micrococci, and that yeasts occasionally form only one spore in the cell.

Nor must we overlook the possibility that the endospore-formation in non-motile bacteria more than merely resembles the development of azygospores in the Conjugatae, and some Ulothricaceae, if reduced in size, would resemble them. Meyer regards them as chlamydospores, and Klebs as "carpospores" or possibly chlamydospores similar to the endospores of yeast. [v.03 p.0157] The former also looks on the ordinary disjointing bacterial cell as an oidium, and it must be admitted that since Brefeld's discovery of the frequency of minute oidia and chlamydospores among the fungi, the probability that some so-called bacteria--and this applies especially to the branching forms accepted by some bacteriologists--are merely reduced fungi is increased. Even the curious one-sided growth of certain species which form sheaths and stalks--_e.g._ _Bacterium vermiforme_, _B. pediculatum_--can be matched by Algae such as _Oocardium_, _Hydrurus_, and some Diatoms. It is clear then that the bacteria are very possibly a heterogeneous group, and in the present state of our knowledge their phylogeny must be considered as very doubtful.

Nearly all bacteria, owing to the absence of chlorophyll, are saprophytic or parasitic forms. Most of them are colourless, but a few secrete colouring matters other than chlorophyll. In size their cells are commonly about 0.001 mm. (1 micromillimetre or 1 ) in diameter, and from two to five times that length, but smaller ones and a few larger ones are known.

Some of the shapes a.s.sumed by the cells are shown in fig. 1.

[Ill.u.s.tration: FIG. 1.--Preparations showing various forms of bacteria and the various types of cilia and their arrangement.

A. _Bacillus subtilis_, Cohn, and _Spirillum undula_, Ehrenb.

B. _Planococcus citreus_ (Menge) Migula.

C. _Pseudomonas pyocyanea_ (Gessard), Migula.

D. _P. macroselmis_, Migula.

E. _P. syncyanea_ (Ehrenb.), Migula.

F. _Bacillus typhi_, Gaffky.

G. _B. vulgaris_ (Hauser), Migula.

H. _Microspira Comma_ (Koch), Schroeter.

J, K. _Spirillum rubrum_, Esmarsch.

L, M. _S. undula_ (Muller), Ehrenb. (_All after Migula._) ]

[Sidenote: Distribution in Time.]

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.

[Sidenote: Distribution in s.p.a.ce.]

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 liquid (blood, urine, milk, beer, &c.) containing organic matter, or any solid food-stuff (meat preserves, vegetables, &c.), allowed to stand exposed to the air soon swarms with bacteria, if moisture is present and the temperature not abnormal. Though they occur all the world over in the s.p.a.ce, air and on the surface of exposed bodies, it is not to be supposed that they are by any means equally distributed, and it is questionable whether the bacteria suspended in the air ever exist in such enormous quant.i.ties as was once believed. The evidence to hand shows that on heights and in open country, especially in the north, there may be few or even no 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 inters.p.a.ces devoid of any, but in laboratories and closed s.p.a.ces 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 ca.n.a.l 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.

[Sidenote: History.]

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.

Muller knew several 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. Conn's brilliant researches, the chief results of which were published at various periods between 1853 and 1872; Cohn's cla.s.sification 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 a.s.sumption 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 cla.s.sification 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 appeals 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.

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) pa.s.ses 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 [v.03 p.0158]

certain number of forms may show different types of cell during the various phases of the life-history,[2] yet the majority of forms are uniform, showing one type of cell throughout their life-history. 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 cla.s.sificatory position its whole life-history 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 ureae_. 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 a.n.a.logies between the phenomena of fermentation and those of certain diseases again made themselves felt, as both became better understood.

Needham in 1745 had declared that heated infusions of organic matter were not deprived of living beings; Spallanzani (1777) had replied that more careful heating and other precautions prevent the appearance of organisms in the fluid. Various experiments by Schwann, Helmholtz, Schultz, Schroeder, Dusch and others led to the refutation, step by step, of the belief that the more minute organisms, and particularly bacteria, arose _de novo_ in the special cases quoted. Nevertheless, instances were adduced where the most careful heating of yolk of egg, milk, hay-infusions, &c., had failed,--the boiled infusions, &c., turning putrid and swarming with bacteria after a few hours.

In 1862 Pasteur repeated and extended such experiments, and paved the way for a complete explanation of the anomalies; Cohn in 1872 published confirmatory results; and it became clear that no putrefaction can take place without bacteria or some other living organism. In the hands of Brefeld, Burdon-Sanderson, de Bary, Tyndall, Roberts, Lister and others, the various links in the chain of evidence grew stronger and stronger, and every case adduced as one of "spontaneous generation" fell to the ground when examined. No case of so-called "spontaneous generation" has withstood rigid investigation; but the discussion contributed to more exact ideas as to the ubiquity, minuteness, and high powers of resistance to physical agents of the spores of Schizomycetes, and led to more exact ideas of antiseptic treatments. Methods were also improved, and the application of some of them to surgery at the hands of Lister, Koch and others has yielded results of the highest value.

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 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 pa.s.sed 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.

[Ill.u.s.tration: FIG. 2.--The various phases of germination of spores of _Bacillus ramosus_ (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.) ]

Other questions of the highest importance have arisen from the foregoing.

About 1880 Pasteur first showed that _Bacillus anthracis_ cultivated in chicken broth, with plenty of oxygen and at a temperature of 42-43 C., lost its virulence after a few "generations," and ceased to kill even the mouse; Toussaint and Chauveau confirmed, and others have extended the observations. More remarkable still, animals inoculated with such "attenuated" bacilli proved to be curiously resistant to the deadly effects of subsequent inoculations of the non-attenuated form. In other words, animals vaccinated with the cultivated bacillus showed immunity from disease when reinoculated with the deadly wild form. The questions as to the causes and 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 Wright, do not here concern us (see II. below).

[Sidenote: Form and Structure.]

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 or not. While some unicellular forms are less than 1 (.001 mm.) in diameter, others have cells measuring 4 or 5 or even 7 or 8 , 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 [Sidenote: Cell-wall.] 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 [v.03 p.0159] cell is always clothed by a definite cell-membrane, as was shown 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_, a.n.a.lysis of the cell shows a large amount of cellulose. The cell-walls in some forms swell up into a gelatinous ma.s.s so that the cell appears to be surrounded in the unstained condition by a clear, transparent s.p.a.ce. 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.

[Ill.u.s.tration: FIG. 3.--Types of Zoogloea. (After Zopf.)

A. Mixed zoogloea found as a pellicle on the surface of vegetable infusions, &c.; it consists of various forms, and contains cocci (a) and rodlets, in series (b and c), &c.