All chlorophyll-free organisms act in a transforming and disturbing manner on the organic compounds from which they obtain their nourishment, and while they themselves grow and multiply, they produce, each after its kind, compounds of a less degree of complexity, i.e. they produce fermentation, putrefaction, sometimes the formation of poisons, and in living beings often disease.
Those organisms which produce fermentation are called ferments; this word, however, is also employed for similar transformations in purely chemical materials (inorganic ferments or enzymes). Many organic (“living”) ferments, among which are Yeast-cells and Bacteria, give off during their development certain inorganic and soluble ferments (enzymes) which may produce other transformations without themselves being changed. Different organisms may produce in the same substratum different kinds of transformation; alcoholic fermentation may for instance be produced by different species of Fungi, but in different proportions, and the same species produces in different substrata, different transformations (e.g. the Vinegar-bacteria oxydize diluted alcohol to vinegar, and eventually to carbonic acid and water).
In the study of Bacteria it is absolutely necessary to sterilize the vessels employed in cultivation, the apparatus, and nutrient solutions, i.e. to free them from Bacteria germs and also to preserve the cultures from the intrusion of any foreign germs (“pure-cultures”). A firm, transparent, nutritive medium is frequently employed. This may be prepared by adding to the nutrient solutions (broth) either gelatine, or—when the Bacteria are to be cultivated at blood-heat—serum of sheep’s or calf’s blood, agar-agar or carragen; serum alone may in itself serve as a nutrient medium. The so-called “plate-cultures” are frequently employed, i.e. the germs are isolated by shaking them with the melted liquid nutrient gelatine, which is then spread on a glass plate and allowed to coagulate; when later on the individual germs grow into colonies, these remain separate in the solid substratum and it is easy to pursue their further development. Similar plate-cultures may also be cultivated in test-tubes and on microscopic slides. The slides and glass plates must be placed in “moist chambers” free from Bacteria. By sowing a few cells (if possible one) using a fine platinum wire, pure cultures for further investigation may be obtained.
In order to prove the relationship between pathogenic Bacteria and certain diseases, the experimental production of pathogenic Bacteria by the inoculation of Bacteria from pure cultures into healthy animals, is very important.
It has not so far been possible to establish a classification of the Bacteria, as the life-history of many species, has not yet been sufficiently investigated.[7] The opinions of botanists are at variance, in many cases, about the forms of growth of a particular kind. Some species are pleomorphic (many-formed) while others possess only one form.
The following Bacteria are Saprophytes:—
Cladothrix dichotoma is common in stagnant and running water which is impregnated with organic matter; the cell-chains have false branching. According to Zopf, Leptothrix ochracea is one of the forms of this species which, in water containing ferrous iron (e.g. as FeCO3), regularly embeds ferric-oxide in its sheath by means of the activity of the protoplasm. Leptothrix ochracea and other Iron-bacteria, according to Winogradsky (1888), do not continue their growth in water free from protoxide of iron; while they multiply enormously in water which contains this salt of iron. The large masses of ochre-coloured slime, found in meadows, bogs, and lakes, are probably due to the activity of the Iron-bacteria.
Fig. 30.—Cladothrix dichotoma.
Those forms which, according to Zopf’s views, represent the forms of development of Cladothrix dichotoma are placed together in Fig. [30]. A represents a group of plants, seventy times magnified, attached to a Vaucheria. The largest one is branched like a tree, with branches of ordinary form; a specimen with spirally twisted branches is seen to the right of the figure, at the lower part some small Leptothrix-like forms. B shows the manner of branching and an incipient Coccus-formation. C a Coccus-mass whose exit from the sheath has been observed. D the same mass as C after the course of a day, the Cocci having turned into rods. E a group of Cocci in which some have developed into shorter or longer rods. F one of these rods before and after treatment with picric acid, which causes the chain-like structure to become apparent. G a portion of a plant with conspicuous sheath, two lateral branches are being formed. H part of a plant, whose cells have divided and form Cocci. The original form of the cells in which the Cocci are embedded may still be recognised. I. Leptothrix-filaments with conspicuous mucilaginous sheath, from which a series of rods is about to emerge; the rod near the bottom is dead, and has remained lying in the sheath. K part of a plant which is forming Cocci, those at the top are in the zooglœa-stage, at the base they are elongating to form rods and Leptothrix-filaments. L a portion of a branched Cladothrix, which divides into motile Bacillus-forms; the rays at the free ends indicate the currents which the cilia produce in the water. M a spirally-twisted, swarming filament, before and after division into halves. N part of a tree-like zooglœa with Cocci and short rods.—All of these spirilla, zooglœa, etc., which Zopf has connected with Clad. dichotoma, are according to Winogradsky, independent organisms.