BACTERIAL NUTRITION 



375 



known to elaborate proteolytic or gelatin-attacking enzymes, 

 as for example B. coli and B. typhi, exert but little influence on 

 the biuret-giving substances of some of the peptones, particularly 



Witte's. 



Commercial peptones are now regarded as being a mixture of 

 polypeptids of all degrees of complexity. It is probable that the 

 peptone fraction of these products contains polypeptids varying 

 in composition from the simplest dipeptids to those which are 

 relatively very complex. The former are more easily utilized 

 as food by the bacteria than the higher or more permanent forms, 



TABLE 5 

 Showing the utilization of Parke, Davis and Company peptone 



OBGANISMS 



Control 



Subtilis group, 3 members 



B. prodigiosus 



P. vulgaris, 2 strains 



P. mirabilis 



Staph, aureus and albus, 4 strains. 



B. cloacae 



B. typhi and B. paratyphi A 



B. coll, 4 strains 



B. diphtheriae, 2 strains 



REACTION 



20.0 

 S.5 

 6.0 

 3.0 



10.0 

 7.5 

 2.0 

 4.0 

 2.0 

 6.0 



SORENSEN 

 TEST 



28.0 

 62.0 

 48.0 

 56.0 

 48.0 

 53.5 

 54.0 

 54.0 

 52.0 

 54.0 



BIURET TEST 



1.0 

 0.0 

 0.0 

 0.0 

 0.7 

 0.6 

 0.4 

 0.6 

 0.6 

 0.5 



Medium : 0.5 per cent peptone, 0.25 per cent beef extract, 0.5 per cent NaCl. 

 Incubation at 30°C. for three weeks. 



and hence disappear from solutions first. ^ As even some of the 

 very simple polypeptids are known to give the biuret color 

 reaction, we may find here a possible explanation of the slow, 

 gradual but lunited reduction in the biuret figures which the 

 non-proteolytic organisms studied brought about. It is the 

 amino acids and other simple nitrogenous substances, however, 

 to which commercial peptone chiefly owes its value as food for 

 bacteria. 



It has been shown repeatedly that meat extract in nutrient 

 broth, etc., contains valuable food substances, and that it is for 



2 Sasaki (1912) has shown that simple polypeptids are attacked by bacteria. 



