Chemical Messengers 85 



about how they work and what constituents of the body they act 

 on. The only clue in this direction so far is the observations by Prof 

 and Mrs Cori in St Louis, that insulin and the secretion of the 

 pituitary gland both affect the action of an enzyme, hexokinase, which 

 is concerned with oxidizing sugar. They act on it in opposite direc- 

 tions, so that the functioning of hexokinase depends on a correct 

 balance between the two. This is one of the first ghmpses we have of 

 a complex interplay of enzymes and hormones through which the 

 bodily functions are regulated and controlled. 



