446 BA CTERIOL OGY. 



These substances were added to sterile litmus agar in 

 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 

 organism they added small quantities of sodium car- 

 bonate. This increase in the salt concentration of the 

 culture medium did not bring about plasmolysis of the 

 typhoid organism. 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 substances. 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 



