PLANT HORMONES 191 



verting them into an entirely new product, or prod- 

 ucts. The essential product of a ductless gland is 

 its hormone at least, that is the supposition and 

 this is probably manufactured by the gland. The 

 indirect proof we have for this statement is that 

 under normal conditions the hormones in the 

 body are sufficient in amount, or sufficiently active, 

 to perform their specific functions; and it is only 

 when a pathological condition sets in that the 

 hormonic function is disturbed. 



You may say that this is not very convincing. 

 You may claim that under normal conditions the 

 gland has the power of removing the hormone from 

 the blood, and that it no longer has such power 

 under pathological conditions. This objection can, 

 I think, be met with in this way: If we examine 

 the constitutional formula for adrenaline, a hor- 

 mone in the adrenals, or of thyroxin, a hormone 

 in the thyroid gland, we shall see that no food 

 we eat contains any such substance. We do, 

 however, find that their formulas show them to be 

 closely related to certain substances that are in- 

 cluded in our diet or at least, are formed in the 

 digestive tract as a result of the food we eat. For 

 example, the amino-acid tryptophane 1 shows cer- 

 tain resemblances to thyroxin; hence the opinion 

 that one of the possible reasons why tryptophane is 



1 See the chapter on Amino-Acids in the author's book on 

 Vitamines. 



