32 L. F. RETTGER, N. BERMAN AND W. S. STURGES 



amount of the inoculating material is introduced to carry with 

 it the necessary enzyme to bring about cleavage of the protein. 

 In a medium containing nitrogen which is directly available, 

 bacterial multiplication will take place, though the number of 

 bacteria introduced is small. If such a medium also contains 

 protein, and if the organism is one which under favorable con- 

 ditions elaborates a proteolytic enzyme, the protein undergoes 

 cleavage as the result of the enzyme action. These points have 

 been demonstrated repeatedly. 



What are some of the important sources of nitrogen avail- 

 able for bacterial metabolism without the aid of an enzyme? 

 Our attention will naturally be directed to aixiino acids which 

 in animal physiology are now known to play such an important 

 part in nutrition. Witte's peptone contains amino acids which 

 may be demonstrated readily by any of the well-known tests, 

 particularly the Sorensen method (Sorensen, 1908). The amount 

 of amino acids present in the American brands of peptone is con- 

 siderably greater than in the Witte product. This undoubtedly ex- 

 plains why we have consistently obtained more luxuriant, though 

 not necessarily more characteristic, bacterial growths in media 

 which contained the American products than in the standard 

 Witte. 



It appears at this time indeed probable that so-called "peptone 

 media" largely owe their value as culture media to the amino 

 acids and perhaps other nitrogenous substances which readily 

 give up their nitrogen as the result of direct bacterial action, 

 and unless bacteria are present which elaborate proteolytic en- 

 zymes, little if any of the proteoses and peptones in the medium 

 is utihzed. Indeed it may be necessary for us to go even further 

 than this, and to adopt the view that the bacterial cell can not 

 utilize any protein until after it has been broken up by some other 

 agent and the nitrogenous portion converted into simple form. 

 If this view should obtain it will be necessary for us to alter 

 materially our conception of the value of peptone, nutrose, and 

 other soluble as well as insoluble proteins as culture media, 

 especially in so far as the group of gelatin-non-liquefying bac- 

 teria is concerned. 



