§2] 



ACCLIMATIZATION TO CHEMICAL AGENTS 



31 



The facts obtained by us clearly indicated, then, that, without 

 selection, — for no deaths occurred in our culture solutions, — 

 the protoplasm may become modified merely by subjection to the 

 poison, so as to gain an increased resistance to it. Hence 

 the acclimatizations that we find in nature need not have 

 been brought about by natural selection — must have occurred, 

 indeed, even without selection, if the organisms had been 

 gradually subjected to their environment. 



go 8EC8. 



Fig. 1. 



40 SECS. 



STRENGTH OF CULTURE SOLUTIONS 



-Curve of resistance periods to a 0.00125% solution of HgCla of Stentors 

 reared in various solutions of HgClg during 20 to 96 hours. 



We did not determine for how long a time the acclimatized 

 Protozoa retained their heightened resistance capacity. The 

 only data we have upon the subject of persistence of acclima- 

 tization is derived from studies on Vertebrates. 



Thus it is the familiar experience of arsenic eaters that, after 

 they have broken off their habit, the body does not quickly 

 return to a normal condition. Even after a considerable period 

 of self-denial the taking of large doses may be recommenced — 

 must be recommenced, indeed, or illness sets in. 



Ehblich ('91) has studied experimentally the phenomenon 



