4l6 HUMAN BIOLOGY 



which has developed innumerable intricate ramifications. 

 But when all is said and done, they all take ultimate root in 

 the antigenic properties of bacterial materials — just as the 

 chemical sciences are basically founded on the electrical 

 laws governing atomic and molecular structure, except 

 that we know considerably less about the antigens and their 

 reactions. 



In regard to the nature of the antigenic substances and 

 in an analysis of the responses aroused by them in the cells of 

 the body we must therefore seek for light concerning one of 

 the most fundamental laws of function of the living cell, 

 physiological in the sense that it is possessed by all of the 

 higher animals as a latent capacity and in that it invariably 

 is called into play in one way or another in the hfe of any 

 individual; abnormal only in the sense that it is probably 

 never in action under conditions of perfect metabolism, a 

 state which, however, cannot be expected to prevail except 

 for short periods in the course of any existence. Whether 

 this emergency reaction capacity should be regarded as a 

 survival of the more primitive properties of a less specialized 

 cellular cooperation, or a function acquired to meet the 

 inevitably frequent entrance of foreign proteins into the 

 animal body is an interesting subject for speculation, but 

 quite unanswerable at the present time. 



Although the term "antigen" was first devised, on an 

 erroneous etymological construction, to designate all sub- 

 stances which were capable of inciting the animal body to 

 the production of antibodies, there is little doubt that 

 the meaning of the word should be more comprehensive than 

 this. At the time when it was introduced investigations 

 upon "hypersensitiveness" were in their infancy and the 

 power of a foreign substance to arouse a specific reaction 

 in the cells of the body was recognized only by the discovery 

 of antibodies in the circulating blood, either by the tech- 

 nique of agglutination, precipitation or "sensitization" to 

 complement. It has since become clear that many substances 

 may alter the specific reaction capacity of the cells without 

 actually leading to the formation of circulating antibodies. 

 The recognition of this state of affairs has come largely 

 through investigations of the strange phenomena of "ana- 



