BACTERIAL NUTRITION 385 



greater than that of others, while the proportion of the albumose 

 and complex polypeptid fraction is correspondingly less. 



The presence of a peptolytic enzyme in cultures of coli, typhi 

 and other gelatin-non-liquefying bacteria has apparently been 

 demonstrated. This erepsin-like enzyme is, however, decidedly 

 weak, and further differs from erepsin of the anunal body in 

 that it does not attack casein. The decomposition of biuret- 

 giving material in commercial peptone is, without doubt, limited 

 to the substances of relatively simple constitution, or the lower 

 polypeptids. This has been demonstrated by the inability of the 

 non-proteolytic organisms in question to attack "purified" 

 proteose, and in a measure by the peculiar shading off of the 

 biuret color, during prolonged periods of incubation, from the 

 characteristic light purple color obtained with a solution of 

 peptone to the deep purple or violet which is given by proteose 

 and albumin solutions with the alkahne copper sulphate. 



It may of course be questioned whether the decomposition 

 of the simple polypeptids of the ''peptone fraction" requires 

 any enzyme action, and whether these substances are not suffi- 

 ciently simple and soluble to be absorbed and utilized directly 

 by the bacterial cell. Such an explanation of the availability 

 of the simple amino acids for bacterial nutrition is quite plausible, 

 since they are very soluble and dialyzable; and further, it would 

 appear improbable that specific enzymes for the many different 

 amino acids are elaborated. 



Even the gelatin-liquefying and proteolytic bacteria are slow 

 to make use of the proteoses and peptone in coramercial "pep- 

 tone." Their initial development is at the expense of the simpler 

 nitrogenous compounds, and a reduction in the biuret-giving 

 substances occurs only after a period of preliminary cultural 

 development, this period often extending over at least a day or 

 two. In this preparatory interval the proteolytic enzyme is 

 formed which is necessary in the utilization of the soluble 

 protein material. That the production of the enzyme which 

 attacks gelatin is as a rule a slow process is well shown in the 

 ordinary gelatin liquefaction tests. 



