384 NATHAN BERMAN AND LEO F. RETTGER 



and 0.5 per cent NaCl added. The media were tubed in 10 cc. 

 quantities, and inoculated with the same organisms used in the 

 preceding tests. The methods of determining the utiHzation of 

 biuret-giving substances were also the same as those employed 

 throughout the earlier work. 



The increased utilization of the predigested peptone was 

 plainly evident. The action of the trypsin almost doubled the 

 amount of nitrogen available for the non-proteolytic organisms. 

 In several instances 65 per cent of the biuret-giving substances 

 of the peptone digestion product was utilized by this group of 

 bacteria, and 35 per cent of the biuret-positive casein digestion 

 product. Aside from the great reduction in the biuret figures, 

 and the high Sorensen titration, the nutrient property of the 

 medium was evidenced by the luxuriance of bacterial growths. 

 It is to be assumed that the large reduction by the gelatin-non- 

 liquefiers in the biuret figure was due to the preponderance of 

 polypeptids of comparatively simple constitution. 



GENERAL DISCUSSION AND CONCLUSIONS 



The results obtained in the present investigation confirm those 

 of previous experiments, and further justify the assumption 

 that bacteria require food substances which are of simple con- 

 stitution and whose properties are such that they readily admit 

 of absorption by the bacterial cell. This view is in harmony 

 with that of Loewi (1902), Abderhalden, etc. as applied to animal 

 nutrition. It furnishes an explanation of the inefficiency of the 

 ordinary laboratory culture media, and particularly solutions of 

 Witte's peptone, for rapid and abundant production of bacterial 

 growth. 



Commercial peptones are highly complex products, con- 

 taining, among other things, different albumoses and so-called 

 peptones, amino acids, particularly the primary, and other 

 simple nitrogen-containing substances. No two brands of 

 commercial peptone are of the same composition, nor is it likely 

 that any one product is uniform. Numerous tests have shown 

 that the amino acid content of some products is decidedly 



