NUTRITIONAL FACTORS IN THE GROWTH OF CERTAIN 

 YEASTS AND BACTERIA. 1 



II. PROTEIN HYDROLYSATES. 



BY LOUIS FREEDMAN 



Biochemical Laboratory of Columbia University at the 



College of Physicians and Surgeons, New York City, 

 and the Research Laboratory of H. A. Metz, New York City. 



INTRODUCTION. 



The use of proteins and protein hydrolysates for enriching 

 culture media for the .growing of bacteria is well known; and 

 we find proteins to be a definite constituent of many culture 

 media. Bainbridge 1 showed that certain bacteria required pro- 

 teins for growth, while Robinson and Rettger 2 used a casein 

 hydrolysate to enrich bacterial media. However, the cases in 

 which it has been definitely shown that the growth of the bac- 

 terial organisms was due to the presence of the protein alone or 

 to any of its hydrolytic cleavage products, are extremely rare. 

 In most cases it has been shown that vitamines were present as 

 an added constituent or as an adhering impurity. 



The possible presence in proteins of a hitherto unknown 

 substance which is now thought to be of biological importance 

 in nutrition, has of late been suggested by several investigators. 

 In this connection, Mueller 3 thought that the growth-stimulating 

 substances for hemolytic streptococci, which he obtained from 

 certain proteins, were definite constituents of the protein mole- 

 cule, and he described the isolation of two such substances from 

 a preparation of enzyme-digested milk proteins called "ami- 

 noids". After his final precipitation of these substances, how- 

 ever, he found them, to be inactive. Goy 4 also described the iso- 

 lation, from certain fungi, of a nitrogen-free acid which he 



1 Read before the Society of Experimental Biology and Medicine. New York City, 

 February 15, 1922. 



