432 BACTERIOLOGY. 



the proportion of 1 to 100, and sterilization was again 

 carried out for five to ten minutes in streaming steam. 



In their studies with these culture media they found 

 that different organisms behaved differently with the 

 lactose. While colon cultures produce a red colora- 

 tion of the litmus when grown on the surface of 

 the medium, the typhoid cultures cause no change. 

 They also found that a culture medium of greater 

 density was of distinct value, and consequently they 

 employed 3 per cent, agar-agar medium, and in order to 

 overcome the marked acid production by the colon organ- 

 ism they added small quantities of sodium carbonate. In 

 order to make the conditions as favorable as possible for 

 the growth of bacillus typhosus they experimented with 

 a large number of artificially prepared albuminous sub- 

 stances. Besides peptone they experimented with tropon 

 and nutrose. The addition of nutrose brought about a more 

 intense blue coloration by the typhoid organism, which 

 they attribute to the alkali albuminate nature of the sodium 

 casein. There was also a more voluminous growth of 

 the typhoid organism when they employed meat infu- 

 sion in the preparation of the medium. 



Still another difficulty was encountered in the identi- 

 fication of bacillus typhosus in stools because of colo- 

 nies of varieties of micrococci also present, which, 

 through their marked acid production, colored the whole 

 surface of the medium. After a large number of nega- 

 tive experiments they succeeded in finding an elective 

 bactericidal aniline dye against the majority of these 

 disturbing organisms, which, however, was not injurious 

 to the typhoid and colon organisms. In the selection 

 of an antiseptic coloring substance they had to be cer- 

 tain that the fermentative properties of the typhoid 

 bacteria were not influenced thereby. They experi- 



