INFECTIONS OF THE DIGESTIVE TRACT 43 



and in many preparations is the exclusive representative 

 of the bifidus type. 



cultural studies. Indeed, the microscopical picture itself shows 

 transitional forms bacilli with slight indications of the accumu- 

 lation of protoplasm at one end and headlet forms which are 

 bifid which look like the simple and the headlet forms. Dumb- 

 bell forms are at times seen in which a headlet has developed at 

 either end of a bacillus. In preparations which have been fixed 

 by heat and treated with Lugol's solution it is possible to demon- 

 strate the presence of granules in the bodies of the bacteria of the 

 bifidus group, located at the peripheral ends of the organism and 

 generally limited to this position. In hanging drops made from 

 fresh material one finds that many of the rod-shaped bacteria 

 possess a sluggish motility which is soon lost. 



Certain relationships between the polymorphous Gram-positive 

 bacteria which dominate the microscopical fields (prepared from 

 the nursling's faecal bacteria) can be made out by means of anaero- 

 bic cultures upon suitable media, such as agar or sugar-agar, 

 containing acid. Pure cultures of the bifidus bacteria are not, 

 however, always quite easy to obtain, as the B. coli group, and 

 some diplococci, which are facultative anaerobes and grow well on 

 the media just mentioned, are apt to restrict the growth of the 

 less hardy bifidus. The development of colonies on sugar-agar is 

 slow, for the tiny white lens-shaped smooth-edged growths first 

 appear in the deeper parts of the sugar-agar after about three 

 days. (Colonies like these in all respects except in having a toothed 

 border are sometimes seen, and consist of mixtures of B. bifidus 

 with B. acidophilus. On further inoculation from such colonies 

 there grows, according to Kahn, only B. acidophilus.) 



On microscopical examination of these colonies, it is apparent 

 that we have to deal with differently shaped bacteria in different 

 colonies and that even in the same colonies there is a tendency 

 to polymorphism. Sometimes the bacilli (always Gram-positive) 

 correspond closely to the simple form already described, both in 

 their form and in the variations in their staining peculiarities. 

 Some colonies are made up of bacteria very much larger than 

 those of the simple form, and frequently knobbed or bifurcated or 

 both. There seems to be little doubt that we are dealing here 

 with various forms of B. bifidus, and the frequent development of 

 bifid and headlet bacteria of varied morphology on the agar medium 



