308 CAUSES OF VARIATION 



SECTION VI EVIDENCE FROM ACCLIMATIZATION 



Considerable light is thrown upon the relative stability of 

 living matter and the extent to which it responds to external 

 influences by the phenomena of acclimatization and the kindred 

 phenomena of immunity. 



Acclimatization to chemicals, especially poisons. 1 " It is clear 

 that the protoplasm of different organisms is dissimilar. We 

 see this in the different reactions to the same chemical agent. 

 Not only is the reaction of the various species unlike, but in- 

 dividuals of the same species from different localities differ 

 widely." 2 



The common poison ivy produces extreme irritation with most 

 persons, the effect being recurrent for many years, while 

 with others it is entirely innocuous. To even the most viru- 

 lent infectious diseases many individuals are entirely immune, 

 and with nearly all diseases of this class a single attack results 

 in immunity for life, through some kind of acclimatization. In 

 much the same manner individuals become accustomed to the 

 sting of bees, and experience little inconvenience from what 

 would have caused intense suffering to most others, or to them- 

 selves before acclimatization. Physicians find it necessary to 

 change their remedies frequently because they soon lose their 

 characteristic effect upon the patient. 



In lower organisms the same phenomenon is noticeable. Thus, 

 " few bacteria can resist i per cent of Na 2 CO 3 , and even the 

 extremely resistant Ascaris lives only [from] five to six hours in a 

 5.8 per cent solution of this salt"; but "Loew has found in 

 Owen's Lake, California (an alkaline water containing, among 

 other things, 2.5 per cent Na 2 CO 3 ), numerous living Infusoria, 

 Copepoda, larvae of Ephydra, and molds." 3 



A solution of acetic acid 0.23 per cent strong kills' the tenta- 

 cles of Drosera, but the vinegar eel lives in a 4 per cent solution. 

 Most protoplasm is extremely sensitive to acids generally, espe- 

 cially to HC1 and H 2 SO 4 ; but the gastric juice is largely HC1, 

 and " the gland cells of some marine Gasteropoda secrete H 2 SO 4 



1 C. B. Davenport, Experimental Morphology, Part I, pp. 27-32. 



2 Ibid. p. 27. 3 Ibid> p . 2 8. 



