264 CAUSES OF VARIATION 



Neapolitan stock were lighter in color than in their native habi- 

 tat, but " none were so light-colored as the ordinary German 

 form." l This difference he ascribes to the cumulative influence 

 of the natural seasonal temperatures, and is quick to protest 

 against its interpretation as indicating an inheritance of acquired 

 characters. He calls it a case of internal selection as between 

 "winter and summer determinants." 



However, that is of no consequence in the present connection. 

 The facts here given show beyond a doubt that outside tempera- 

 tures exert a direct effect upon so important a character as 

 color. Whether this occurs by chemical disturbance in pigment 

 formation, by internal selection, or by other means does not 

 greatly matter here. There is some evidence tending to show 

 that the light color of polar animals is due to the direct action 

 of cold. 2 This, if true, argues for chemical action upon pigment 

 as the cause of color changes due to temperature. 



Temperature an all-pervading influence. Temperature differs 

 from most other external forces in being, for many species, at 

 least, an all-pervading influence. Higher animals and plants 

 are themselves centers of heat production, and in general their 

 temperatures are the algebraic sum of their own heat production 

 and the heat of their surroundings. Lower organisms, however, 

 are very largely dependent upon their environment for their 

 temperatures, and in cases of this kind the entire protoplasm of 

 the body is affected. 



SECTION VIII EFFECT OF CHEMICAL AGENTS UPON 

 PROTOPLASMIC ACTIVITY 



All development, all differentiation, and all functional activity 

 of living organisms are the result of protoplasmic activity ; but 

 protoplasmic activity is, in the last analysis, chemical activity, 

 and it is certainly subject to many of the laws controlling ordi- 

 nary chemical reactions. It is noticeable in the study of vital 



1 Weismann, Germ Plasm, pp. 399-400. 



2 The writer has somewhere read that animals on shipboard become rapidly 

 lighter in color as the coat becomes exposed to intense cold, but he is unable to 

 verify the report. 



