Chapter XVII 

 ADJUSTMENT TO INFECTIOUS DISEASE 



Hans Zinsser 



WHEN one living unit implants itself on the surface 

 or within the tissues of another, the result of the 

 association must be either a mutual adaptation, 

 degrees of which, are spoken of as "commensulism" and 

 "symbiosis," or a struggle determining the deftruction of 

 one or the other of the reacting organisms. The processes 

 which are initiated and by which the invaded unit depends 

 itself have been analyzed particularly in connection with 

 infectious diseases of man and animals. But in order to 

 understand them properly it is important to remember 

 that the powers of adjustment and defense which are set 

 in motion have a biological significance far broader than its 

 apphcation to the accidents of infection. They represent a 

 deep-seated emergency mechanism latent in the normal 

 body, an ancient heritage of the cytoplasm by which living 

 cells and tissues are enabled to meet abnormal metabolic 

 conditions of any kind and to preserve themselves from 

 injury by the entrance into their substance of any materials 

 that cannot be utilized nutritionally. Since many of these 

 methods of defense are shared in common by the higher 

 animals and plants and the simplest Kving units like pro- 

 tozoa, Ehrlich has picturesquely spoken of them as Uralte 

 Protoplasma Weisheit. 



Infection is in itself a distinctly abnormal process, or 

 perhaps better, an accident in the plan of nature. The 

 term "normal," when applied to the physiological processes 

 of the higher animals, is of course, like "infinity" in mathe- 

 matics, an entirely abstract conception. Nevertheless, it 

 is necessary to formulate it as a working basis, for the purpose 

 of properly defining deviations. Thus, it is a normal ten- 

 dency in nature to preserve the integrity of biological units, 

 and the parasitism of one living individual upon the sub- 

 stance of another may be regarded as an abnormal occur- 

 rence which implies either struggle or adaptation; and here, 



406 



