314 CAUSES OF VARIATION 



Acclimatization to electricity. It is matter of common knowl- 

 edge that individuals working about electricity and accustomed 

 to frequent shocks acquire a high resistance power. Exact data 

 are not at hand, but of the general fact there can be no doubt. 



Acclimatization in general. It is matter of common experience 

 that among the higher animals and plants extreme changes in 

 locality may be followed by any one of three separate conse- 

 quences : first, unprecedented prosperity from extremely suit- 

 able conditions, conditions even more favorable than in the 

 native habitat ; second, absolute failure from sheer inability to 

 endure the changed conditions ; and third, a period of struggle, 

 followed by a more or less complete adaptation to new condi- 

 tions, a process known everywhere as acclimatization. 



The known facts concerning adaptation in lower forms seem 

 to apply in the same direction, if not to the same extent, to 

 even the highest known species. For example, the biennial of 

 the temperate regions becomes perennial in the tropics, where 

 all distinctions of this order blend and disappear and where all 

 plants live until they die from other than climatic causes. This 

 is a sufficient explanation for the more ready formation of fleshy 

 roots and stems in northern regions, and the lesser storage of food 

 reserves in the tropics, where growth tends to be continuous. 



It has always been held that plants have higher powers of 

 acclimatization than have animals. Doubtless this is true, at 

 least so far as purely climatic conditions are concerned, because 

 animals, being free to move and gifted with more or less intelli- 

 gence, are able in a considerable degree to avoid the full effects 

 of climate by seeking shelter or protection of some sort. Their 

 own bodies are fitted to maintain, even against fearful odds, a 

 nearly constant temperature. So far as temperature is concerned, 

 therefore, animals do not need the same degree of adaptation as 

 do plants, which must endure the best they can the " accident of 

 position." Whether the animal possesses the same capacity for 

 acclimatization, whether it is capable of undergoing the same de- 

 gree of alteration and developing the same resistance, is another 

 question, but experience with poisons tends to show that the animal 

 organism is not inferior to the vegetable in point of adaptability 

 when put to the actual test and compelled to face the inevitable. 



