AEROBIC SPORE-BEARING NON-PATHOGENIC BACTERIA 279 



already mentioned. The organisms frequently regarded as 

 Bacillus subiilis which are characterized by their greater size, 

 their soft mealy growths on hard media, and their thick friable 

 scums we agree with Chester in referring to the "cereus" group 

 the principal type of which, Bacillus cereus, was first described 

 by the Franklands. There are two strains of Bacillus cereus 

 differentiated by their action on saccharose but it does not 

 aeem wise at the present time to divide the species. Our identi- 

 fication of Bacillus cereus rests upon Chester's work and upon 

 cultures sent us by him several years ago. In addition a num- 

 ber of strains of Bacillus cereus have been received from American 

 laboratories and from the Krai collection in Vienna, all of them 

 agreeing with Chester's in their reactions and thus furnishing 

 us a distinct type by means of which our own strains were identi- 

 fied. Bacillus cereus is the most widely distributed aerobic 

 spore-bearing organism in nature in Baltimore and vicinity, 

 as it seems to be in other localities, and possibly has more syno- 

 nyms than any other species. With these types of Bacillus 

 suhtilis and Bacillus cereus clearly outlined the task of identify- 

 ing the other spore-bearing organisms became somewhat simpler. 

 Bacillus vulgatus was soon found so frequently as to enable us 

 to recognize it without difficulty. One strain of this organism 

 was obtained from the Winslow collection in New York. When 

 freshly isolated the vulgatus is very characteristic and differs 

 entirely from other species. The strains isolated in Baltimore 

 were identical with the organisms found in Montreal several 

 years ago and regarded there as Bacillus vulgatus and give 

 reactions ascribed to the widely distributed ''potato bacillus." 

 Bacillus mesentericus {B. mesentericus fuscus) was recognized by its 

 morphology and its cultural reactions. In this species we follow 

 Chester. In one instance we obtained a stock culture of Bacillus 

 mesentericus which gave the correct reactions as outlined by 

 Chester, this culture coming from the laboratory of hygiene of 

 the University of Pennsylvania. Bacillus pumilu^ of Gottheil 

 we do not regard as a distinct species. Bacillus aterrimus (B. mes- 

 entericus niger) was identified by its production of a black or 

 grey-black pigment, its cultural reactions resembling those of 



