230 VITALISM AND SCHOLASTICISM 



quite true. " As far as we can judge," says 

 Balfour Stewart, " life is always associated with 

 machinery of a certain kind, in virtue of which 

 an extremely delicate directive touch is magni- 

 fied ultimately into a very considerable trans- 

 mutation of energy." That we may look upon 

 as an assured fact, but we have still to consider 

 whether the " directive touch " is a form of 

 energy_. In this connection we cannot neglect 

 the important subject of catalysis, the name 

 given to chemical actions brought about by a 

 substance which is called the " catalyst," which 

 substance is, after the action is over, recovered 

 unaltered. For a complete account of this 

 matter, works on chemistry must be consulted, 

 but as a concrete example it may be mentioned 

 that platinum either in sheet or in spongy form 

 will cause or hasten action without itself under- 

 going any kind of change detectable by the 

 chemist. And so with other bodies from which 

 it appears that action may be caused or directed 

 by a body which itself undergoes no change. 

 In the living body something very similar seems 

 to take place with regard to the products of the 

 endocrine glands such as the thyroid, thymus, 

 adrenal and others. 



These products are known as hormones, and 



Hormones their discovery has cleared up the difficulties 



which have for long been felt as to the use 



