The first observer who perceived bacteria was van Leeuwenhoek. As early as 1675, while examining by chance with his magnifying glasses a drop of putrid water, the father of microscopy remarked with profound astonishment that it contained a multitude of little globules, which moved with agility. The following year he recognized the presence of bacteria in faeces and in tartar from the teeth ; and, if he has not named them, it is easy to assure one's self by the description which he has given of their form and of their movements, and by the figures which accompany these descriptions, that the organisms observed by him are truly Bacteria, Vibrios, and perhaps even Leptothrix.
In 1773 0. F. Muller endeavored to classify these organisms. He made of them a group of infusoria, under the name of Infusoria crassius cula, and established two genera, the g. Monas and Vibrio ; the first characterized as follows : " vermis inconspicuus, simplicissimus, pellucidus, punctiformis,". The genus Vibrio " vermis incon spicuus, simplicissimus, teres, elongatus" enclosing under thirty-five specific names, with the true bacteria, some organisms belonging to other classes of the animal and vegetable kingdoms.
In the classification of the infusoria given by Bory de Saint-Vincent in the " Encyclopedic Methodique" (1824) and afterwards in the " Dictionaire Classique d'Histoire Naturelle" (1830) the bacteria are distributed in two different families of the microscopic gymnodae, the monadaires and the vibrionides. Besides the monads, properly so called, of which the Monas termo has been preserved by the greater part of the bacterologists, the monadaires include some veritable infusoria, which have no relation with the monads. It was the same with the vibrionides, of which the genera Vibrio and Mellanella included some beings very different in their organization. Indeed, beside some veritable vibrios, bacteria, and spirilla, constituting the genus Mellanella, Bory placed some nematoid worms, such as the Anguillula of vinegar.
With Ehrenberg (1838) and Dujardin (1841) the family of the vibrioniens was established upon characters more homogeneous, and their species upon distinctions truly scientific. But these two observers, followed in this by M. Davaine, deny completely the affinities of the elongated bacteria (Bacterium, Vibrio etc.) with the punctiform bacteria ( Monas] ; and it is necessary to come to the time of MM. Hallier, Hoffmann, Cohn, and the greater number of recent botanists, in order to see these two forms brought together anew.
In fact, Ehrenberg defines his vibrioniens, which he arranges between the volvocinece and the closteria " animals, filiform, distinctly or apparently polygastric, no mucous membrane, naked, without external organs, with the body (like monads) uniform and united in chains or filiform series, as a result of incomplete division." He included in this class all filiform bodies gifted with proper movement and formed of articles, dividing them into four genera :
1. Bacterium: filaments linear and inflexible; three species.
2. Vibrio : filaments linear, snakelike, flexible ; nine species.
3. Spirillum : filaments spiral, inflexible ; three species.
4. SpirocTicete : filaments spiral, flexible; one species.
A fifth genus, including but one species, the Spirodiscus fulvus, with filaments in a helix, in flexible, disposed in contiguous layers, has not been seen since Ehrenberg. Let us add that Ehrenberg often attributed to them a complex structure, stomachs more or less numerous, a pro boscis, cilia serving as organs of locomotion, all characters that more recent observers have failed to find. Nevertheless, we must make an HISTORICAL. 17 exception in favor of the cilia, of which the ex istence has been recently verified in the case of several of the bacteria by divers botanists, among others by MM. Cohn and Eug. Warming.
Dujardin (1841), in his " Histoire Naturelle des Zoophytes/' preserved the family of the vibrioni ens of Ehrenberg among the infusoria, characteriz ing them as follows : " filiform animals, extremely slender, without appreciable organization, without visible locomotive organs." He made but few modifications, of which the principal consisted in uniting Spirochceta with Spirillum, Dujardin. Rejecting the character that Ehrenberg drew from the rigidity of the spirilla, the Spirochceta pllca t'dis, Ehrb. Became the Spirillum plicatile, Duj. ; but, as will be seen later, this change has not been maintained. Dujardin, then, classed the bac teria in :
1. Bacterium : filaments rigid, with a vacillating movement.
2. Vibrio: filaments flexible, with an undulatory movement.
3. Spirillum : filaments spiral, movement rotatory.
Until this time the bacteria had been considered as animals placed at the foot of the series. Subsequently the tendency to place them in the vegetable kingdom became more and more pronounced.
Already, since 1853, M. Ch. Robin had pointed out the relationship of the bacteria and of the Vibrios with Leptothrix. This opinion, which was not favorably received by the authors who adopted nearly all of the generic groups of Ehren berg and Dujardin, is to-day accepted by many botanists, above all since the labors of Cohn. (See below: classification.) At all events, it is to M. Davaine (1859) that we are indebted for clearly pointing out that the vibrioniens are vegetables, nearly allied to the algae, and especially to the confervas.
This same author, having observed some mo tionless bacteria, thought it necessary to give this character great consideration, and to estab lish a fourth group, the genus Baeteridium, which he added to the three others admitted by Dujar din ; but in this creation he was less happy than in his placing the vibrioniens among the vege tables ; for we shall see further on that this char acter of mobility or of immobility is not absolute, and that it depends upon the age of the bacterium or upon certain conditions relating to the medium in which it is placed.
The most recent complete exposition of the classification and of the ideas of M. Davaine is found in the " Dictionnaire Encyclop. Des Sci ences Mdicales," art. Bacteries (1868). It may be summed up as follows : Filaments straight or bent, but not in a spiral .
Moving sponta-) Rigid. . BACTERIUM.
Neously . . J Flexible . VIBRIO.
Motionless .... BACTKKIDIUM.
Filaments spiral SPIRILLUM.
The genus Bacterium comprises six species, S. termo, catenula, punctum, triloculare, or articula tum, already described by Ehrenberg and Dujar din, and B. putredinis and capitatum, new species of M. Davaine, established, the first for a bacte rium producing rot in plants, the second for a spe cies, swollen at the extremity, observed in some macerations.
The genus Vibrio includes twelve species,
V. lineola, tremulans, rugula, prolifer, serpens, bacillus, synxanthus, and syncyanus of previous authors and the V. lactic, butyric, and tartaric right, discovered by M. Pasteur in these different fermentations.
In the genus Bacteridium, M. Davaine places five new species, the " Bacteridies charbonneuse, intestinale, du levain, glaireuse, et des infusions."
He includes also the ferment which, according to
M. Pasteur, occasions the " sickness of turned wine."
Finally, the genus Spirillum includes the species S. undula, tenue, volutans of Ehrenberg, S. rufum and leucomcenum of Perty, and S. plicatile, Duj.
From this moment the history of the bacteria enters upon a new phase. The labors of M. Pas teur upon the inferior organisms and their role in fermentation, the researches of MM. Davaine and Hallier upon the bacterium of charbon, and the micrococci of contagious maladies, call the atten tion of chemists and of pathologists to these or 20 THE BACTERIA.
Ganisms and especially to the bacteria. Their origin, their evolution, the physiological peculiarities of their nutrition and reproduction, are the object of numerous labors, and give rise to passionate discussions relating to the subject of spontaneous generation, polymorphism of fungi, theories of fermentation, and the pathology of virulent and infectious maladies. For this reason an exposition of these researches, often contradic tory, is extremely difficult. We will make it suc cinctly, insisting especially upon the labors relating to the classification of the bacteria, and reserving to ourselves the privilege of returning to the his tory of several points, when we approach their study in the special chapters of this thesis.
The first important memoir published after that of M. Davaine upon the bacteria is that of
M. Hoffmann, in 1869. He demonstrates : First, that the bacteria are plants, having a very distinct cellular organization ; second, that they can only be classified in accordance with their form and size, at first into monads and linear bacteria, and the latter into microbacteria, mesobacteria, and megabacteria ; (M. Hoffmann includes with the linear bacteria, Vibrio, Bacterium, and Leptotlirix, which are bacteria united in a chaplet ;) third, that mobility or immobility is not a specific char acter, but may present itself in the same species under the influence of changes of temperature, of density of medium, etc. M. Hoffmann studied also the origin of the bacteria, and rejects the hypothesis of a spontaneous generation. As to HISTORICAL. 21 their role in the phenomena of the decomposition of organic bodies and in fermentations, M. Hoff mann confesses " that, with the exception of yeast and of the acetic and butyric ferments, all the rest is still enveloped in obscurity."
M. Cohn is the naturalist who, has occupied himself the most with the bacteria. In 1853, he published his first researches upon this subject. The genera Zoogloea, which he established at this time for the bacteria arranged in gelatinous masses, diffused or more or less crowded together, was not a happy creation. It was adopt ed at first by M. Rabenhorst who, in his work on the fresh-water algae of Europe, places them after the palmellaceae, while he classes the other bac teria, Vibrio and Spirillum, in the family of the oscillatoriae. The Zooglcea were later abandoned by their author as a generic group, and are preserved only as the name of one of the diverse transitory stages through which the bacteria pass in .the course of their evolution (Zooglcea, Leptothrix, Toruld).
Twenty years later the same savant commenced the publication of a series of " Memoirs " upon these organisms (in his " Beitrage zur Biologie der Pflanzen"). In the first paper the author gives an exposition of his researches upon the organization, development, and classification of the bacteria, and upon their action as ferments.
M. Cohn considers them as a well-defined group, the schizospores, belonging to the algae, at the commencement of the series of the phycochromacese, with several families with which the different genera of bacteria have many affinities. He recognized, however, that the absence of chlorophyll approaches them, at least from a functional point of view, to the fungi. Upon this point we may say that for other botanists this character is de cisive, and the bacteria are classed as fungi.
M. N'ageli, who takes this view, describes them under the name of Schizomycetes. Cohn divides the bacteria into four tribes, comprising six genera :
1. The Sphcerobacteria or globular B.
2. The Microbacteria or rod B.
3. The Desmobacteria or filamentous B.
4. The Spirobacteria or Spiral B. We will return to this classification.
In 1874, M. Th. Billroth, in his researches upon the Coccobacteria septica, expressed opinions en tirely different from those of Cohn. According to Billroth, the bacteria differ considerably in form according to the medium in which they are placed and divers circumstances. He claims that they constitute but a single species, the Coccobacteria septica. This vegetable organism can pre sent itself under the form of globular articles (coccos) or under that of rods (bacterie). These two forms may reproduce themselves by becoming elongated and dividing transversely, or may pass the one into the other. Billroth claims to have found both forms united in a single filament, a fact which in his opinion demonstrates conclusively their relationship. Each of these two forms can also present variations of size, in ac cordance with which he establishes the following divisions : Micrococcos Microbacteria.
And varieties of association which give rise to the following names : Monococcos Monobacteria.
Streptococcos Strep tobacteria.
The following year (1875), Cohn, in the second part of his " Researches " upon the bacteria, criti cised the opinions expressed by Billroth in the preceding memoir. Cohn believes that we should regard as distinct genera and species all the bacteria having a particular form and acting differently as ferments, so long as the proof of their identity has not been demonstrated in an evident manner. Coming back also to the affinities and classification of these organisms, he insists anew upon their near relationship to the Phycochromacese; and, no longer distinguishing the bacteria as a special family, he distributes his different genera in a group, which he calls Schizopkytes, which includes the greater part of the R Chrococcece and of the Oscillarice. We will return to this subject when we speak of the classification of the bacteria.
In 1876, appeared in the same number of Cohn's " Beitrage " two important papers. The first, by Cohn, treats of the influence of temperature upon the bacteria, of their origin, of the formation of spores ;n the Bacillus of. Hay infusion, and of charbon. The second, by Koch, gives the result of his researches upon the bac teria of charbon, the Bacillus anthracis.
Koch has been able by skilful cultivation to follow the complete development of this Bacillus, and to witness the formation of spores, of which the vitality is very great, and which are the principal agents of the transmission of this terrible malady.
I must still indicate, in addition to these special works, a quantity of notes and of memoirs scattered through the reviews and periodical publications.
The list will be found in the bibliography ap pended to this work. I must also cite the recent work of M. Nageli upon " The Inferior Fungi and their Role in Infectious Maladies." The learned professor of Munich has studied the diverse fungi which produce decompositions. He divides them into three groups, the Mucorini, the Saccharomycetes, and the 8M0ompcetes, which correspond to the bacteria. According to Niigeli, the bacteria are fungi which produce putrefac tion.
In presence of these opinions, so diverse, as to the nature of the bacteria and their classification, we will finish by saying with Cohn : " So long as the makers of microscopes do not place at our disposal much higher powers, and, as far as possible, without immersion, we will find ourselves, in the domain of the bacteria, in the situation of a traveller who wanders in an unknown country at the hour of twilight, at the moment when the tight of day no longer suffices to enable him clearly to distinguish objects, and when he is conscious that, notwithstanding all his precautions, he is liable to lose his way."