[Illustration: FIG. 21.—Agar Milk Sugar. Colony of _Bacterium W._ from Yoghourt (non-granular variety of the granule bacteria, as far as possible identical with Luersen and Kühn's _Bacillus bulgaricus_), of a cubical branching-out form.
According to Kuntze, the granule formation of this and related organisms is variable, while White and Avery regard it as a constant characteristic. (Incubated two days at 37° C. Magnified x 50.)]
[Illustration: FIG. 22.—Two colonies of _Bacillus acidophilus_ from calf's manure. Agar Milk Sugar Culture. With this organism, also, we have conformation to one type of colony, while, in other respects, temperature requirements and production, etc., we have close agreement with the granule bacillus (_Bacillus bulgaricus_). (Two days at 37° C. Enlarged about 1:50.)]
[Illustration: FIG. 23.—Beer-wort Gelatine. Fourteen-days-old colony of Yoghourt yeast. (Enlarged about 1:50.)]
[Illustration: FIG. 24.—Shredded preparation of the Bulgarian original Yoghourt. Stain: aqueous methylene blue. Granule bacillus, diplostreptococci, and yeast. (See also other photo-micrographs of Yoghourt. Enlarged 1:70.)]
[Illustration: FIG. 25.—Granule Bacillus from Yoghourt. Cultivated in skim milk in twenty-four hours at 37° C. Stain: aqueous methylene blue. (Enlarged 1:50.)
By means of this staining treatment the presence of granules (not spores) can be easily detected. Treatment with fuchsine fails to bring out these formations.]
[Illustration: FIG. 26.—_Bacteria W._, Agar Milk Sugar Culture. Cultivated twenty-four hours (knobs, clubs). Stain: Gram's method coloured with aqueous fuchsine afterwards. (Enlarged 1:600.)]
[Illustration: FIG. 27.—_Bacteria acidophilus_ from calves' manure, isolated by means of bouillon as acid as vinegar. Shredded out of the usual Agar culture. Twenty-four hours at 37° C. Stain: aqueous methylene blue. (Enlarged 1:700.)]
[Illustration: FIG. 28.—Mucus from calf's stomach inoculated into milk after eight transferrings. Shredded preparation cultivated in milk for twenty-four hours at 37° C. Diplostreptococci and granule bacillus. Stain: aqueous methylene blue. (Enlarged 1:500.)]
[Illustration: FIG. 29.—Diplostreptococcus from Yoghourt. Pure culture in skim milk. A comparison of the illustrations will show how close a resemblance exists between bacteria found in the mucous membrane of calf's stomach and those occurring in Yoghourt. In fact, by the combined action of granule bacilli, and of diplostreptococci from calf's stomach, together with a Yoghourt yeast, it is possible to prepare normal Yoghourt.]