BACTERIAL NUTRITION 



379 



development. The beef extract was not sufficient to supply the 

 initial needs of these organisms for enzyme production. The 

 proteus group is known to find poor growth conditions in syn- 

 thetic media, particularly the Uschinsky medium. The staphy- 

 lococcus forms affected the biuret-giving substances but very 

 little, if at all. The members of the Coli-typhi-paratyphi 

 group, furthermore, were unable to attack the purified proteose, 

 during the entire incubation period of three weeks. The Sorensen 

 values strongly support those of the biuret test. 



An experiment was conducted to determine whether proteose 

 is attacked in a medium in which it furnishes the sole source of 

 nitrogen. The test solution consisted of approximately 0.25 



TABLE 10 

 Showing the behavior of bacteria in dialyzed Witte's peptone 



ORGANISMS 



B. subtilis 



B. prodigiosus. 



B. typhi 



B. coli 



Control 



BIURET 

 TEST 



1.0 

 0.0 

 1.0 

 1.0 

 1.0 



Medium: 0.25 per cent "proteose," 0.5 per cent NaCl. Chemical tests made 

 after incubation of three weeks. 



* X indicates too many colonies to count. 



per cent proteose and 0.5 per cent NaCl. The medium was 

 employed in small Erlenmeyer flasks in 50 cc. quantities. The 

 technique was essentially the same as in the experiments with 

 native proteins and with coagulated egg albumin. Bacterial 

 counts were made by the plate method, immediately after inocu- 

 lation and after definite intervals. Biuret and Sorensen deter- 

 minations were also made. The results are given in table 10. 

 They indicate that proteose resists direct bacterial attack, and 

 thus falls in the same group with the native proteins and coagu- 

 lated egg albumin. 



B. prodigiosus, as in the, experiments on native proteins, was 

 able to develop in the test medium. This may be explained by 



