AEROBIC SPORE-BEARING NON-PATHOGENIC BACTERIA 281 



factor to the changes seen in milk pasteurized at lower tempera- 

 tures, 60° to 65°C., which subsequently develops a bitter taste. 



Bacillus mycoides was identified without difficulty by the 

 classical descriptions and by the work of Chester whose con- 

 clusions were based upon a culture which was sent him from our 

 laboratory several years ago. The felted growths in the depths 

 of agar are very characteristic and are given by but one other 

 species, Bacillus ramosus-liquefaciens oi Prausnitz. 



For a long time we were in doubt as to the identification of the 

 very large microorganisms which are placed in a heterogeneous 

 group and sometimes called Bacillus megatherium, sometimes 

 Bacillus petasites, and sometimes Bacillus tumescens. The 

 first member of this group was described by De Bary (1884, 

 1887) whose illustrations are very characteristic. Many of the 

 cultures identified and sent to us as Bacillus megatherium differed 

 radically from De Bary's description, and Chester's conclusions 

 in regard to the ill-defined character of the group seemed to be 

 entirely justified. These large organisms were very abundant 

 however and soon resolved themselves into two distinct types. 

 One type agreed with De Bary's original description in aU 

 essential particulars and this type agreed also with an isolation 

 of Bacillus megatherium by Kellermann sent us from the Winslow 

 collection. Two cultures of Bacillus tumescens of Zopf agreed 

 closely with this Bacillus megatherium and there seems to be no 

 reason to regard it as a distinct species. The other type has 

 almost the same morphology and the same cultural reactions as 

 Bacillus megatherium but produces an intense yellow pigment. 

 This type corresponds to the organism recently described as 

 Bacillus petasites by Gottheil. All the organisms thus far en- 

 countered with the morphology referred to can thus easily be 

 divided into these two main forms. The Bacillus graveolens of 

 Gottheil, not the Bacillus graveolens of Bordoni-Uffreduzzi, 

 seems to be merely a strain of Bacillus megatherium in which the 

 bacilli have a pecuHar property of growing in short spirals. It 

 has not been encountered in our work. 



The Simplex-cohaerens group of Chester proved possibly the 



