﻿74 FREER. 



we observe are brought about by chemical substances present in the host, 

 or by -what is still more likely, a combination between certain definite 

 substances in the introduced cell and of otbers in the host. If now we 

 consider the development of various races from their simplest beginning, 

 we are forced to the conclusion that, in the struggle for existence and in 

 the adaption of individuals to environment, a great variety of substances 

 of gradually increasing complexity must be formed which take part not 

 only in assimilating food but in resisting the encroachments of parasitic 

 organisms. In proportion as, through the ages, the conditions surround- 

 ing the race have been altered, as the attacks have multiplied, and the 

 means of resisting them have been applied, there has sprung up the vastly 

 complex chemical system of the higher organisms, and, as the materials 

 which these organisms must assimilate are varied and the means which 

 they must take to resist destruction are also of great variety, it follows 

 that those chemical bodies which in the host are capable of the destruction 

 of the invader must also be great in number. It is not possible, consider- 

 ing the specific character of the destruction of certain cells, that one chem- 

 ical individual should bring about the various types of immunity, indeed, 

 if immunity were due to one chemical individual we would expect it 

 to be universal, and universal immunity would imply the destruction 

 within the body itself of its own tissues, namely, autolysis. Furthermore, 

 the cell which is introduced is in itself resistant in some organisms, non- 

 resistant in others, it may itself therefore have developed immune bodies 

 which must differ from the immune body in the host. We must therefore 

 come to the conclusion that a multitude of chemical groups or individuals 

 must exist in any one organism, which are calculated to resist the invasion 

 of foreign cells. Another question, entirely, is that of the chemical 

 complex or possibly the transference of energy which renders the attack- 

 ing chemical body active. This factor in the destruction of the foreign 

 cell might be uniform throughout, for its action is through the chemical 

 complex which is only one of the destroying factors. If it is simply a 

 method of producing a change of energy it is difficult to conceive why 

 it should act at one time and not at another or, if it is a uniform chemical 

 body, why it should in the sera of certain cases be destroyed at a low 

 temperature and in others at a higher one. 



From what has gone before we must conclude . that the development 

 of race immunity is a process of heredity, that the substances which confer 

 certain types of immunity on the individuals of a given race have been 

 produced by a course of development concomitant with the other mani- 

 festations of evolution and that the chemical bodies which confer the 

 immunity in individuals must be vast in number. In reaching this 

 conclusion we must not lose sight of another means by which immunity 

 can be conferred, namely by the absence of groups capable of uniting 

 with introduced cells or toxins — but this phenomenon also must be the 

 result of heredity. 



