252 MEDICINE 



salvarsan. In another direction treatment has 

 attained to a wholly rational basis. When, as the 

 result of disease, the body lacks a product made 

 normally by itself the missing product may be 

 directly supplied. The administration of sheep's 

 thyroid gland to the cretin, first practised by 

 Dr Murray of Newcastle, is an instance of treat- 

 ment, magical in its results, but utterly rational in 

 respect of its basis. 



The third great line of advance towards rational 

 treatment has followed the teaching yielded by the 

 experimental study of natural immunity. Parasites 

 such as bacteria kill, not by their mere presence 

 in the body, but because they produce poisons. 

 Now the body itself nearly always reacts to the 

 poison of the parasite so as to produce a substance 

 capable of either neutralising the poison or killing 

 the poison producers. The human body may fail, 

 however, to produce such substances with sufficient 

 rapidity, and it then succumbs to the attack of 

 the enemy. What could be more rational than 

 to assist it by giving the very same protective 

 substances obtained from animals which have been 

 so treated as to produce them in excess ? This is 

 the modern serum treatment, which, together with 

 treatment by vaccines, a method based upon 

 allied but somewhat different principles, has already 

 secured great triumphs. It is a very new thing, 

 however, and when developed will show triumphs 

 greater still. In therapeutics, then, the experi- 



