538 NATHAN BERMAN AND LEO F. RETTGER 



40 per cent of the original ''protein" in the peptone solution, 

 even under the most favorable conditions, as for example the 

 addition of ammonium sulphate, asparagine, glycerine, phos- 

 phates, etc. In some instances 10 to 20 per cent marked the 

 maximum reduction. When other peptones were employed, 

 however, namely five different American brands, reductions con- 

 siderably in excess of 40 per cent of the protein were frequently 

 obtained. In all of these experiments the Sorensen method gave 

 corroborative results. 



Media containing Witte's peptone which had been dialyzed 

 for at least two days underwent less change in their protein con- 

 tent than the corresponding solutions of untreated peptone. Fur- 

 thermore, the so-called ''proteose fraction" obtained from Witte's 

 peptone by precipitation with ammonium sulphate, repeated pre- 

 cipitation with sodium sulphate, and prolonged dialysis, was 

 apparently unattacked when used in place of the original com- 

 mercial peptone. The results obtained thus far indicate that 

 the gelatin-non-liquefying organisms of the Coli-typhi-paraty- 

 phi group are unable to utilize or in anyway affect the proteose 

 portion of commercial peptones. 



In the light of the researches of Emil Fischer and his pupils 

 (2) on polypeptides, the deportment of the Bacilus coli type 

 of gelatin-non-liquefying bacteria towards commercial peptone 

 may be explained as follows. These peptones, far from being 

 relatively simple, are mixtures of many organic substances of 

 varying composition and complexity, particularly amino acids 

 and polypeptides. Some of these polypeptides are in all prob- 

 ability quite simple, as for example the condensation product 

 of two simple amino acids, and if we accept the conclusions drawn 

 by different investigators, others are of a much more complex 

 type, and are tied up with the peptone and proteose molecules. 

 Some of the polypeptides give a positive biuret reaction, even 

 the relatively simple ones, while others are negative to this test. 

 All may on decomposition yield ammonia, amines and amino 

 acids. 



The proteose fraction of commercial peptone, it may be as- 

 sumed, contains the relatively complex polypeptides, and hence 



