AGf~ICULTURAL RESEARCH, PUSA.

858 PRAcTICAL BACTERIOLoGY
(vide p.l22). The colonies are small, and vary in appearance
as seen under the low power of the microscope;
two main types arc described: (1) "feathery," in ap"
peamnee not unlike a B. tctani colony, and (2) rounded
with projecting outgrowths (" crab-colony"). A convenient
method of obtaining cultures from faeces
is to inoculate broth to which is added 0·5 per cent.
of' glacial acetic acid; after incubation subcultures
can be made on agar plates under aerobic conditions.
This organism produces acid fermentation of glucose
and lactose without gas formation. It also ferments
maltose, whereas B. bulgaTicus, a related OTganism
originally isolated from Yoghurt (a fermented milk),
has no action on maltose. The latter organism
cannot grow in the intestine of man. Other allied
organisms are B. acidophilIts odontolyticus, described
in association with dental caries, the so-calleel Boas"
Oppler bacill'Us found in the stomach contents in
conditions in which hydrochloric acid is absent or
deficient, and Dodet·ldn' s bacill'Us which is found
normally in the vagina.
BACILLUS BIFIDUS (Bacteroides bifirbm)
Derives itH name from the apparently bifid appearance
described by the original observers. This organism is found in
large numbcrs in the faeces of breast-fed infants. Its average
dimensions are 4-5", by 0'7jL, but it shows considerable pleomorphism.
The ends are often swollen. Three bacilli together
may be arranged like a Y. Though usually Granl-positive,
there is a certain amount of variation in its reaction to Gram's
staining method.
In primary culture it ifl a strict anaerobe. Cultures have
been obtained at 37° C. in tubes of neutral lactose-broth
containing a piece of sterile rabbit kidney (vide p. US) with a
layer of sterile vaseline superimposed on the medimn. After
several days' growth, subcultures are Illude on glucose agar,
Illates of which arc incubated anaerobically. Purc cultures
in glueose agar can be obtained from single colonies. The
organism may ultimately be grown aerobically.