CULTIVATION OF THE BACILLUS 75 



Growth, however, took place with lo per cent, of 

 glycerine, and in the presence of a much higher per- 

 centage of salt; but in the complete absence of glycerine 

 growth was not nearly so good. It was found better 

 to dry the tubercle bacillus after killing it, and before 

 making it up into medium. This was done in vacuo 

 over caustic potash. The improvement in this case 

 may have been due to the formation of breaks in the 

 continuity of the covering of the bacillus, thus allowing 

 the " essential substance " to diffuse more easily into 

 the medium. Of the dried bacilli, J to i per cent, 

 was found to be sufficient to add to the ^gg medium. 

 Alterations in the normal alkalinity of the egg medium 

 produced no good results. The bacillus seems to 

 prefer a slightly alkaline medium. 



In a further series of experiments the dead tubercle 

 bacilli were added to ordinary glycerine - agar and 

 glycerine-broth, but these media did not, as a rule, 

 give such good results, though glycerine-peptone-beef 

 broth, containing J to i per cent, of dried tubercle 

 bacilli, gave a fairly satisfactory growth. In the case 

 of the subcultures on the agar medium, growth occurred 

 along the needle-track as small, white, elevated colonies, 

 which at first were smooth and discrete, but after six or 

 eight weeks they coalesced and presented an irregular 

 surface. When older, the growth turned a dull yellowish- 

 white, and in tubes with a single colony this spread 

 and became more heaped up in the centre, while the 

 margins were thinner and irregular. The growth, 

 although slow, was very similar to that of the tubercle 

 bacillus. The growth in the broth subcultures occurred 

 as tiny granules at the bottom of the flask, and these 

 little masses of bacilli increased in size and number, 

 though very slowly. At the end of six months one 

 flask showed a very thin film on the surface of the 



