278 J. S. LAWRENCE AND W. W. FORD 



The cultures identified by us as Bacillus subtilis corresponded 

 in all particulars to a culture sent us several years ago by Chester 

 and kept in the laboratory since then. The particular points 

 by which Bacillus subtilis may be differentiated from Bacillus 

 vulgatus are the development on glucose litmus agar where it 

 forms a dry hard warty growth made up of dense masses of 

 material clinging firmly to the medium, in which may be ob- 

 served numerous blebs or blisters containing milky fluid, and 

 on Loeffler's blood serum where a similar growth appears, often 

 however with a distinct red color. On both glucose litmus 

 agar and blood serum Bacillus vulgatus develops as a soft 

 wrinkled friable mass easily broken and lifted from its sub- 

 stratum. On potato the subtilis differs from the vulgatus. 

 The former produces at first a rather dense whitish or greyish 

 mass often showing blebs similar to those on agar and blood 

 serum, a distinct red line appearing in the potato a little dis- 

 tance from the growth, from which characteristic the name 

 Bacillus subtilis-ruber is frequently employed. After 48 to 72 

 hours a wrinkling appears, the growth later becoming moist and 

 homogeneous. B. vulgatus produces a wrinkled growth from the 

 start, this becoming extremely abundant in 3 to 4 days and 

 frequently assuming a decided pink color. The differences 

 between the two species are somewhat difficult to describe but 

 when potato cultures of the organisms are placed side by side 

 the points of differentiation become clear and definite. In 

 general the subtilis cultures are dry and hard on solid media and 

 produce firm tenacious scums on fluids, while the vulgatus cul- 

 tures are soft and mealy and their scums friable and easily broken. 

 On a morphological basis it is extremely puzzling to attempt the 

 differentiation of the two types. In general the rods of Bacillus 

 vulgatus are longer and thinner than those of Bacillus subtilis 

 while the spores are flatter and bulge the organism only a little 

 if at all. 



This view of Bacillus subtilis of Cohn and the interpretation 

 put on Cohn's work by Chester is not entirely accepted 

 by bacteriologists but we feel convinced of its correctness 

 except in regard to the differentiation from Bacillus vulgatus 



