574 WILLIAM S. STURGES AND LEO F. RETTGER 



of these biuret-containing substances the results of such action 

 would be revealed in subsequent tests. In fact, it is more than 

 possible that the bacterial cells contain relatively simple biuret- 

 giving polypeptides which have been absorbed from the medium 

 or which are intermediate synthetic products occurring in the 

 natural course of bacterial metabolism. Berman and Rettger 

 (1918) showed that Bad. coU is unable to utilize the more com- 

 plex or proteose fraction of Witte's peptone, but that some of 

 the simpler biuret-containing substances in the commercial 

 peptone, probably polypeptides, are attacked by pure culture 

 of this organism and broken down into the simpler amino acids. 



Furthermore, it is doubtful whether very slight increases in 

 amino nitrogen need necessarily indicate any hydrotysis. We 

 may be dealing with more or less masking of amino nitrogen by 

 the protein, which does not allow all of the amino nitrogen to 

 react in the Van Slyke procedure, during the early part of the 

 incubation period. Such a protective action may to a certain 

 extent be removed by such purely phj^sical processes as diffusion, 

 partial disintegration from osmotic disturbance, toluol extrac- 

 tion, etc. Changes of this type would render the amino acids 

 more and more available during the course of incubation for 

 the Van Slyke determination. Such influences scarcely seem 

 suflficient, however, to explain the more pronounced increases 

 in amino nitrogen noted in some of the experiments, as for ex- 

 ample in chart 6 where the increases are shown to range from 4 

 to 60 per cent. 



The failure to demonstrate marked changes in the suspensions 

 of Bad. coli by the biuret, Sorensen, Van Slyke and conduc- 

 tivity methods is fully supported bj^ direct microscopic examina- 

 tions of the different suspension during the periods of observa- 

 tion. The individual cells at all times took the ordinary stains 

 well and with a high degree of uniformity, and there was no 

 evidence of morphological change, except in Via of the second 

 series of experiments which also differed markedly from all 

 others in its reaction to the biuret, Van Slyke and conductivity 

 tests, and which must be excluded from serious consideration 

 on account of the probabiUty of bacterial contamination. 



