/l/ Diets containing all amino acids produce slightly better growth than 

 mixtures of "required" constituents alone. L- forms are biologically ac- 

 tive. /2/ D-form of the amino acid inactive. /j/ Cltrulline can par- 

 tially substitute for arginine. /k/ Required for maximal growth. /5/ 

 D-form of the amino acid active. /6/ In non- sterile cultures. /?/ Re- 

 quired by males only. /8/ D-Serine extremely toxic, and L-Serine slightly 

 toxic. /9/ Requirement or lack of requirement not demonstrated since 

 valine was present in yeast extract, one of the ingredients of the med- 

 ium. 



24 



