CLASSIFICATION I I 



display of their powers. It has long been known that the nervous 

 system has control not only of the stimuli which promote function, 

 but also of those inhibitory activities which are essential to the 

 regulation of the working economy. 



That many chemical substances present in the body also 

 exercise this inhibitory influence is a discovery of very recent 

 date. 



We know, from Loeb's interesting experiments, that certain 

 activities of muscles, nerves, and glands, especially the muscular 

 irritability which manifests itself as rhythmic contraction, depend 

 upon the presence under certain conditions of Na-, K-, Ca-, 

 and probably also Mg-ions ; and that every change in the 

 relations of these ions changes the properties of the tissues. A 

 sudden change in the relationship of the ions will, according 

 to the nature of the change, bring about either stimulation or 

 inhibition of function. 



The Ca-ions, which are necessary to all life, act as inhibitors 

 of muscular activity, and Loeb draws attention to the fact that, if 

 it were not for the presence under normal conditions of Ca-ions in 

 the blood, the skeletal muscles of the body would be in a state 

 of constant rhythmic contraction. 



If, then, certain organs produce substances which are 

 inhibitory to the activity of other organs, it is obvious that failure 

 on the part of an organ to provide its inhibitory material may 

 give rise to symptoms similar to those of poisoning. 



Having obtained definite proof that in certain tissues sub- 

 stances are formed which, by acting as chemical stimuli, bring 

 about a decreased activity on the part of other organs in other 

 words, they exercise an inhibitory influence upon functional activity 

 we are in a position to abandon the hypothesis of auto- 

 intoxication and to adopt that of the presence of inhibitory 

 hormones. This theory attains its highest measure of probability 

 when we find it supported by the results of organo-therapy ; 

 when, in fact, the disturbances which regularly ensue upon the 

 cessation of any organic function, may be prevented or even cured 

 by the administration of the extract of that organ or of the 

 chemical material obtained from it. 



In those cases where organo-therapy has failed, while the 

 symptoms of suppression have disappeared upon the direct trans- 

 plantation of the organ, the results have usually been ascribed 

 to an antitoxic activity. But this conclusion is by no means 

 incontestable. The transplantation of an organ is a method which 

 closely reproduces the natural conditions and, where successful, 

 restores the organ to the body in its natural structure and function. 

 All that has happened is that the organ in question has, to a 

 certain extent, changed its locality. The medical method 

 is, in reality, a substitute for the surgical and is a less perfect 

 and less certain imitation of natural measures. Where the extract 



