664 GASTRO-INTESTINAL BACTERIOLOGY 
intensely; the remainder of the rod stains faintl}' or not at all. At 
first sight these granules resemble chains of cocci. This somewht 
pleomorphic organism is B. bifidus, first observed by Escherich, but 
isolated in pure culture and studied in detail by Tissier.^ It is an 
obligate anaerobe,' fermentative in character, which typically forms 
considerable amounts of acid from lactose and other sugars, but no 
gas. The organism received the name "bifidus" from its remarkable 
property of developing well-defined bifid ends when it is grown in 
artificial media; it does not ordinarily exhibit bifid ends in the intes- 
tinal tract. Moro^ and, independently, Finkelstein"* have isolated and 
described an organism very similar in morphology to B. bifidus as 
it occurs in the intestinal contents, but which differs materially from 
the latter both in its aerobiosis and in its inability to develop bifid 
ends in artificial media. This organism, B. acidophilus, is more 
Fig. 101. — Bacillus bifidus. Sediment from lactose fermentation tube. X 1000. 
commonly found in the intestinal contents of artificially-fed babies 
than in nurslings, and it is more tolerant of organic acids than B. 
bifidus. It belongs to the group of Aciduric Bacteria.^ 
In addition to B. bifidus'' and B. acidophilus, which typically com- 
prise a majority of the characteristic intestinal bacteria, smaller 
numbers of Micrococcus ovalis, B. coli, B. lactis aerogenes and other 
bacteria are found in the feces of nurslings. 
Cooke^ has isolated and described a Gram-positive, aerobic, non- 
1 Recherches sur la Flore Intestinale des Nourrissons, etc., Th^se de Paris, 1900, p. 85. 
2 Noguchi (Jour. Exp. Med., 1910, 12, 182) states that Bacillus bifidus, under labora- 
tory conditions, may become aerobic and form spores. 
3 Wien. klin. Wchnschr., 1900, 13. 114. 
* Deutsch. med. Wchnschr., 1900, 26, 263. 
6 Kendall: Jour. Med. Res., 1910, 22, 153. Rahe: Jour. Infec. Dis., 1914, 15, 141. 
Kendall and Haner: Jour. Infec. Dis., 1924, 33, 89. 
« Madam Tsiklinsky (Ann. Inst. Pasteur, 1903, 17, 217) has not been able to demon- 
strate B. bifidus in normal nurslings' feces as frequently as has been reported elsewhere; 
the consensus of opinion appears to be, however, that bifidi are the most characteristic 
bacilli of the normal nursling intestinal flora. 
" Am. .Jour. Dis. Child., 1921, 22, 481; Jour. Bacteriol., 1927, 13, No. 5. 
