ADJUSTMENT TO INFECTIOUS DISEASE 417 



phylaxis" and "allergic hypersensitiveness." These occur- 

 rences can best be explained by examples. Antigenic 

 substances like horse serum and egg albumen when injected 

 into normal guinea pigs may cause no reactions whatever, 

 though given in considerable amounts. The material itself 

 is entirely inocuous. If, however, the first administration is 

 followed in the course of two or three weeks by a second 

 injection of the same material, severe injury of the animal 

 may result. Since the original material was harmless, it is 

 obvious that some change was brought about in the animal 

 as a result of the first contact; and the state reached is 

 known as "specific hypersensitiveness" or, in the case of the 

 complete proteins, "anaphylaxis." An animal so sensitized 

 will react only to the particular material with which it has 

 been prepared. If, for instance, one guinea pig is given egg 

 white and another horse serum, a subsequent injection of 

 horse serum into the "egg white animal" will be entirely 

 uneventful, and vice versa. But a repetition of the identical 

 material into the same animal will arouse a response apparent 

 both by local edema, possibly tissue destruction, and by 

 systemic symptoms which may cause death within a few 

 minutes. It is quite impossible to summarize these reactions 

 by any generalization since they vary with the several 

 animal species and are subject to differences dependent upon 

 dosage and the intervals between injections. Physiologically 

 the poirit of attack appears to lie chiefly in the capillary 

 endothelium, which is rendered permeable as a result of 

 the reaction, and there is reason to believe that the further 

 complex train of events which is set in motion in other, 

 parts of the body is secondary to this primary injury. 



But while there is much that is obscure about the actual 

 causes of injury and death in such cases, it is quite clear 

 that the process is set in motion by union of the reinjected 

 antigen with antibodies that were formed in the animal as a 

 result of the first injection. These antibodies, remaining to 

 some extent incorporated in the cells that formed them, 

 have acquired, in consequence, a greatly enhanced capacity 

 for union with the antigen; and this sudden introduction of a 

 foreign protein into or upon the surface of the tissue cells, 

 particularly of the reticulo-endothelial system, results in 



