175 



vious experiment, on a broth-agar medium containing easein- 

 tryptone (1 part Cole & Onslow's „stock broth" -f- 2 parts 

 broth free from salt, sugar, and peptone, + 2% agar), to which 

 after sterilisation pepsin-digested blood was added. This me- 

 dium was put into large test tubes and sloped. All the strains 

 gave a fairly good growth. After 4 days' incubation the con- 

 tents of the tubes were melted, and a little distilled over by 

 boiling, the indol reaction being carried out on the distillate. 

 In this way I achieved 2 things: (1) the assurance that 

 there actually was a growth of Pfeiffer's bacillus in the cul- 

 tures; (2) the production of a more sensitive reaction. In an 

 orientation experiment it had been shown that the positive 

 reactions were strongest when they were done with the distilled 

 liquid. The indol passes over with the first fraction of the 

 distillate and it will therefore be found in greater concentra- 

 tion in this than in the original culture. 



With this mode of procedure the reactions were also negative 

 with the following exceptions: Ms 4, H 127, H 205, H 314c and GP 5. 



Plate cultivations of these strains were then prepared and ino- 

 culations were made in tubes of haemoglobin broth and the solid 

 medium described, from various colonies that appeared. After 4 

 days' incubation the reaction was tested on the broth cultures and 

 on the distillate from the agar cultures. 



The results were as follows: 



