CLASSIFICATION OF ACIDURIC BACTERIA 409 



Bacillus bulgaricus were isolated from milk in but two instances, 

 fourteen other strains proving to be aciduric organisms of 

 another type. 



The Bacillus acidophil-aerogenes of Torrey and Rahe (1915) 

 is an aciduric organism differing from the bacillus of Moro in 

 that it forms gas. The Bacillus bifidus is easily identified upon 

 morphological grounds. Opinion as to its anaerobic require- 

 ments has lately undergone modification (Howe, 1917) . We know 

 that the characters just mentioned differentiate the organisms 

 in some fashion, but when as groups, and when as individual 

 bacilli, has never been determined. The object of the present 

 investigation is to determine whether a better classification 

 might not be made. 



The methods employed in this work were, with some modifi- 

 cation, those used by the writer in his earlier investigations in 

 this field. The selective medium was acetic acid-glucose-broth 

 having an acidity of n/20. This was seeded with the material 

 under examination and incubated for three days. The method 

 of triple seeding employed by Kendall (1910) was early aban- 

 doned, confirmation of the aciduric nature of the organisms being 

 obtained by primary cultivation in this broth of the colonies 

 fished from agar plates. Unneutralized glucose-oleate agar was 

 superseded by the glucose liver agar of Torrey (1917). This 

 medium has a reaction of plus 3. 



In the cultivation of the bacteria of the type of B. acidophilus 

 incubation for two or three days is desirable, though this is not 

 always necessary. All cultures were carried in the unneutra- 

 lized meat-peptone-glucose broth, and, with the various test 

 substances substituted for glucose, this broth was used in the 

 cultural tests. The Bacillus bifidus was grown in 0.5 per cent 

 glucose agar having an acidity of plus 2. The strains of this 

 organisms were isolated in part from human and in part from 

 canine stools. The new differential plating method devised by 

 Torrey (1917) was employed for this purpose. 



It will be seen upon reference to the table that the cultures 

 examined were obtained from a variety of sources. In saliva 

 the Bacillus acidophilus and the Bacillus _ acidophil-aerogenes 



