600 NEW AND UNIDENTIFIED GROWTH FACTORS 



animal kingdom, with the probabihty that many important new meta- 

 bolites may be exposed to view, and the assurance that our knowledge of 

 comparative biochemistry will be greatly enriched. Though many of these 

 metabolites may come to fall outside the biocatalyst class, it is neverthe- 

 less the continued unveihng of metabolic machinery to which the investi- 

 gators in this field are dedicated, and their progress will be followed keenly 

 by all who would gain an insight into the economy of the cell. 



