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.]

In a review of the literature of the subject of soured milks, Makrinoff
suggests the adoption of the two names, _Streptobac. lebenis viscosus_
and _Streptobac. lebenis non-viscosus_, for the organisms of the
so-called Bulgaricus group, and known at present as
_Bacillus-bulgaricus_, _Streptobac. lebenis_, _Bacillus of Massol_,
_Granule bacillus_, _Bact. Mazun_, _Bac. lactis acidi_, etc.[77]

White and Avery[78] have made a comparative study of a large number of
varieties and species of lactic acid bacteria of the above type obtained
from various fermented milks and milk tabloids. Their descriptions are
so detailed and their conclusions are so important that we give them at
length. According to this work, the whole of the thermophilic lactic
acid bacilli of the so-called Bulgaricus type may be divided into two
sub-types, A and B.

_The Cultural Characteristics of the Bacillus Bulgaricus Group_

The cultural characteristics of all the strains of _Bacillus bulgaricus_
(granule bacillus) are as follows:

_In Whey Agar._--All strains exhibit wide variation in size, 2 mu to 50 mu
long and about 1 mu broad.

Almost all individuals are intensely Gram-positive, and show regularity
of outline. All strains show involution form, exhibiting vacuoles, and
often show empty cell membranes. The latter are Gram-negative, and vary
greatly in both dimensions as well as in form. All strains show tendency
to chain formation, some being arranged in chains of six to twenty-five
segments, which may contain both Gram-positive and Gram-negative
individuals. Type B exhibits Gram-negative spherical bodies varying from
0.25 mu to 1 mu in size, adhering to the sides of some of the
Gram-negative individuals.

_In Whey._--In this medium there is a marked tendency toward
degeneration and involution. In the early stages of incubation, at 100 deg.
to 112 deg. F., the bacilli are uniform in size and inten