Vol. IX. August, lyoj. No. 3 



BIOLOGICAL BULLETIN 



IMMUNITY AND ADAPTATION. 1 



LEO LOEB. 



Various writers, in discussing the phenomena of adaptation, 

 included among them the fact that in many cases organisms be- 

 come immune against certain injurious influences, as for instance 

 the action of toxic substances, provided that these influences were 

 active during a sufficiently long period ; the immunity against 

 disease-producing bacteria was especially 'regarded as a phe- 

 nomenon of adaptation. These writers, therefore, explained 

 immunity by including it among the larger class of adaptive 

 phenomena. Although this attitude appears from a certain point 

 of view as the most rational one, it may nevertheless in other 

 respects be more fruitful to adopt the opposite attitude, which 

 consists in trying to gain an insight into the mechanism of cer- 

 tain adaptive phenomena, by making use of the discoveries made 

 in the course of investigations in immunity. This attitude seems 

 also justified by the fact that a large number of instances of ac- 

 quired immunity cannot be directly explained as adaptive phe- 

 nomena. In these respects, therefore, the conception of immunity 

 is wider than that of adaptation. 2 The main reason for taking the 

 second attitude, however, lies in the fact that the phenomena of im- 

 munity have been partially at least accessible to an experimental 

 analysis, much more so than other phenomena of adaptation. 

 The latter may be conveniently classified as internal and ex- 



1 From the Pathological Laboratory of the University of Pennsylvania. 



2 T. H. Morgan in his book on " Evolution and Adaptation " includes the phe- 

 nomena of immunity among the adaptive processes. He expresses, however, the 

 view that certain of these phenomena could not be explained as due to any selective 

 processes. The following remarks, the partly hypothetical character of which is 

 quite apparent, were written with the aim of connecting a number of somewhat iso- 

 lated facts, and of suggesting the possibility of an extension of such considerations 

 to different fields of investigation. 



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