THE MYCOLOGY OF THE CHAPTER I. BACTERIA are minute unicellular organisms forming the lowest group of the Cryptogams, or flowerless plants, and are the intermediate link between the animal and vegetable kingdom of living things, related on the one hand to the Mycetozoa, or animal fungi, on the other to the Algae. They are divisible into two groups, a higher and a lower. The lower, known as Schizomycetes, or fissionfungi, are most numerous, comprising the greater number of the organisms with which pathological mycology deals. They are all microscopic in size, and are rarely more than in. in one direction. To facilitate general description mycologists have adopted a standard of measurement designated micron = 1oo part of millimetre, or 2500 part of inch, which is written μ, the dimensions of an organism being expressed as multiples or fractions, e.g., " 2.5 μ long, 0.75 μ wide." The lower group of bacteria consists of the relatively monomorphous varieties, which are classified according to their shape: (a) small globular bodies, occurring singly or associated with others, designated cocci; (b) rod-shaped forms known as bacilli; (c) spiral or corkscrew forms, and the curved fragments of the same, called spirilla. The term bacterium is properly applied to microorganisms of the schizomycetal group generally, and is used as such in the present work. The higher bacteria are relatively pleomorphous, and may exhibit real or pseudo-branching as in Cladothrix dichotoma; their method of reproduction as well as their form is allied to the moulds, whilst some of the stages in their life cycle are indistinguishable morphologically from the lower group of fissionfungi. The bacteria as a group are most active chemical agents, splitting up effete animal and vegetable matter into bodies assimilable by plants, fixing free nitrogen as on the roots of Leguminosa, and assisting in the disintegration of the hardest rocks. A limited number produce disease in both animals and plants, and finally van Tieghem claims to have demonstrated the presence of the bodies. of bacteria in coal, where their activity was concerned in the rotting of the old coal forests. Classification.-Bacteria belong to the vegetable kingdom, and are placed under the sub-group of Thallophytes, one of the divisions of the Cryptogams, thus: The fungi may be divided into two main groups according to their mode of growth. Fungi { Schizomycetes Fission-fungi. Higher fungi, generally branching. The above scheme gives the general position of the bacteria, but it is extremely difficult to properly classify all the organisms generally included in the term "bacteria"; more particularly is this the case with those species-of which Actinomyces may be taken as an example-which are related to the true Schizomycetes on the one hand and to the Eumycetes on the other. Most of the forms with which bacteriology has to do belong however to the Schizomycetes, and it is necessary for convenience of description to adopt a classification. The grouping generally adopted is Baumgarten's, a modification of that first suggested by Cohn, based upon morphological form, and although not entirely scientific is at present the most convenient. Various other methods of classification have been suggested by different observers; thus Du Bary and Hueppe adopt a classification based on spore formation: (1) those bacteria forming endogenous spores; (2) those forming exogenous or arthrospores. Our knowledge of sporulation is as yet too imperfect to adopt such as a method of classification. Another source of confusion is the different meaning which authors attach to their terminology; for instance, bacterium is used as a general term including bacteria generally; Hueppe uses it in the limited sense of those organisms which do not produce endogenous spores, the term bacilli being applied to the spore-forming species. Migula calls motile organisms bacilli, non-motile ones bacteria. I have adopted the commonly accepted meaning of bacillus as a rod-shaped organism, and the term bacterium or bacteria as a general one. Considerable confusion also exists regarding the loosely applied term leptothrix, some meaning thereby a thread or special morphological form which is common to a considerable number of species. Zoph, who first used the term, applied it to a distinct species of the higher bacteria, and it is in this sense it is used in the following pages. Chester ("Determinative Bacteriology ") suggests the following classification: COCCACEE. I.-Cells unbranched, or showing only false branching as in Cladothrix. (a) Cells globular, becoming slightly elongated before division, which takes place in one, two, or three dimensions. BACTERIACEAE. (b) Cells short or long, cylindrical, straight, curved or spiral, without sheath; motile or non-motile; endospores present or absent. CHLAMYDOBACTERIACE. (c) Cells surrounded by a sheath and arranged in elongated filaments. BEGGIATOACEÆ. (d) Cells not surrounded by a sheath, arranged in filaments and motile by means of an undulating membrane. MYCOBACTERIACEÆ. II. Cells short or long, cylindrical or filaments, clavate, cuneate, or irregular in form. Without endospores, but with formation of gonidia-like bodies by segmentation of the cells. Without flagella. Division at right angles to the rod or filament. Not possessed of sheath, but having true dichotomous branching. For grouping of species see Chester ("Determinative Bacteriology,” p. 54). Lehmann and Neumann suggest the following arrangement :— (1) Coccacea. (2) Bacteriaceœ. (3) Spirillaceæ. (4) Corynebacterium, Diphtheria bacillus. (5) Mycobacterium, acid fast organisms (tubercle bacillus). (6) Actinomyces. 66 Cladothrix, Crenothrix, and Leptothrix are classed as Higher fissionfungi." In both these classifications the genus Bacteriaceæ are divided into two classes : (a) Bacterium-not forming endospores. (b) Bacilli—forming endospores. For further information see Lehmann and Neumann (p. 119 et seq.), where proper principles for nomenclature of bacteria are laid down. The Lower Bacteria.-(a) Cocci-round, oval, or elliptical cells ranging from 0.5 to 2 μ in diameter. When not spherical the greatest diameter is not greater than twice the lesser. They are not possessed of motility but often exhibit considerable Brownian movement (p. 11) with the exception of a few species (e.g., Micrococcus agilis of Cohn, Malta fever coccus). Reproduction is by binary fission, and spore formation (endogenous) is unknown. In some cocci, particularly the streptococci, large swollen elements with increased refractive power are often to be seen; these have been described by Du Bary as a mode of sporulation under the term arthrospores (fig. 1, d.) The cocci are arranged into groups according to their mode of reproduction. (1) STREPTOCOCCI.-Division (binary fission) occurring regularly in one plane only, the individual elements remain attached by their capsules in the form of chains; in some species the chains may attain great length and be composed of a large number of individual cocci. (2) STAPHYLOCOCCI.-Division occurring irregularly in one plane only, the cocci remaining attached by their capsules in irregular clumps and masses, compared to bunches of grapes. The number of species in these two groups is very large. The formation of arthrospores is well marked (Du Bary). (3) DIPLOCOCCI.-Division in one plane regularly, the cocci |