IMMUNITY. 169 



CHAPTER VII. 

 IMMUNITY. 



Studies in immunity have led to remarkably uniform results 

 in so far as the facts are concerned. All agree on the actual 

 observations, both of the processes which take place spontane- 

 ously in nature, as well as of those which follow in intentional 

 experiments. There is, however, great difference of opinion 

 upon the interpretation of these phenomena, and several 

 opposing theories have been advanced in regard to the mechan- 

 ism concerned, each theory finding very eminent supporters. 



In view of these facts, it is necessary, in discussing immunity, 

 to give a definition covering its broadened application, to cite 

 the observations which have been recorded and to present 

 the prevalent explanations offered by the various authorities, 

 omitting various theories now abandoned. 



Immunity as formerly studied embraced only considerations 

 of the insusceptibihty of individuals or of races to an attack 

 of a given infectious disease. But the modern conception is 

 broader than this, and it is no longer confined to immunity 

 proper, but extends to certain other processes which have been 

 found to bear a close resemblance, in certain respects, to 

 immunity, and to be governed by laws very similar to those 

 which govern the latter. 



Immunity at present is made to include besides insuscepti- 

 bility to infection — i. e., resistance to the invasion of hving 

 bacteria — the processes concerned in the forming of the anti- 

 bodies, antitoxins proper, antiagglutinins, antilysins and 

 antiprecipitins. 



IS 



