386 NATHAN BERMAN AND LEO F. RETTGER 



The ability to liquefy gelatin is not in itself a proteolytic or 

 even a gelatinolytic function, for some organisms which can 

 liquefy gelatin are unable to carry the change beyond the gela- 

 tose stage, and fail to decompose ''purified" proteose and casein. 



Members of the coli-typhi-paratyphi group of organisms 

 studied are without ability to decompose gelatin and casein. 

 They are unable also to affect the "proteoses" in commercial 

 peptone, and in their reduction of the biuret-giving substances 

 attack and decompose only the simpler of these components, 

 presumably the lower polypeptids; the action on even these 

 relatively simple substances is slow and delayed. Bacillus 

 cloacae is not here included in the above group of organisms, 

 though its action in the media containing the above substances 

 is almost, if not entirely, the same as that of B. coli, etc. 



The value of a cultural medium for bacteria depends on the 

 immediately available food substances which it contains. For 

 this reason it appears quite reasonable thai those commercial 

 peptones which contain the largest amount of amino acids and 

 other nitrogenous products of simple composition are most con- 

 ducive to active and abundant bacterial development, every 

 thing else being equal. This supposition is fully borne out by 

 experiment. The question as to whether such peptones are the 

 most satisfactory for toxin production in a medium requires 

 further and extensive intestigation. 



The conclusions may be summarized briefly as follows: 



1. Bacteria are unable to decompose coagulated native pro- 

 tein when there is no other source of available nitrogen in the 

 test medium. 



2. There is reason to believe that purified proteose also is 

 resistant to direct attack by bacteria. 



3. Gelatin-non-liquefying bacteria and some of the liquefiers 

 are feeble in their action on Witte's peptone. A much better 

 utilization of the biuret-giving substances occurs in media con- 

 taining commercial peptone which has been subjected to more 

 extensive digestion in the process of preparation, as for example 

 certain of the American brands. 



