168 PTEROYLGLUTAMIC ACID 



growth measured by titration of the acid produced. Assays with S. faecalis 

 can be made in 16 hours, and the growth measured turbidimetrically or by 

 titration after 40 hours incubation. A method has been developed by 

 Roberts and SnelP'^ by using L. casei with a 16 to 24-hour incubation period. 

 A trypsin digest of casein is used in the basal medium which serves as a 

 source of strepogenin and permits maximum growth of the organism to be 

 reached in a short time. 



VII. standardization of Activity 



E. L. R. STOKSTAD 



The ease of microbiological assay has prevented extensive use of animal 

 assays for the measurement of pteroylglutamic acid. Chicks and rats are 

 used on occasion to determine the total pteroylglutamic acid activity for 

 animals. This affords a partial answer to the problem of whether the micro- 

 biological methods are a true measure of the pteroylglutamic acid activity 

 for animals. 



Two methods have been proposed for chick assay. One is a curative test^ 

 in which the sample is administered orally in six doses given every other 

 day. The increase in hematocrit is used as a measure of the response. A 4- 

 week prophylactic test using a purified type of diet of chemically defined 

 ingredients has been also used.^- ^ 



Rats cannot be made deficient in pteroylglutamic acid by the simple ex- 

 clusion of this factor from the diet. By the use of sulfonamides, such as 

 sulfaguanidine or succinylsulfathiazole, in the diet it is possible to produce 

 a pteroylglutamic deficiency in this species. An assay method based on this 

 type of diet has been proposed in which growth is used as the criterion of 

 response in rats. 



VIII. Occurrence in Foods 



E. L. R. STOKSTAD 



The distribution of PGA in foods is shown in Table IX. The data present 

 a summary of information compiled by the Bureau of Human Nutrition 



" E. C. Roberts and E. E. Snell, /. Biol. Chcm. 163, 499 (1946). 



1 B. L. O'Dell and A. G. Hogan, /. Biol. Chem. 149, 323 (1943). 



2 C. J. Campbell, R. A. Brown, and A. D. Emmett, J. Biol. Chem. 154, 721 (1944). 



3 C. J. Campbell, M. M. McCabe, R. A. Brown, and A. D. Emmett, Am. J. Physiol. 

 144, 348 (1945). 



