302 The Influence of Environment 



sively of two variables, the mass of enzymes for the 

 chemical reactions underlying the heart-beat and the 

 temperature. By inheritance the mass of enzymes is 

 approximately the same and in this way all the embryos 

 beat at the same rate (within the limits of the fluctuat- 

 ing variation) at the same temperature. This identity 

 exists, however, only as long as the embryo is relatively 

 quiet in the egg. As soon as the embryo begins to 

 move this equality disappears since the motion influ- 

 ences the heart-beat and the motility of different 

 embryos differs. 



In man the number of disturbing factors is so 

 great that no equality of the rate for the same tem- 

 perature can be expected. Differences in emotions 

 or the internal secretions following the emotions, 

 differences in previous diseases and their after-effects, 

 differences in metabolism, differences in the use of 

 narcotics or drugs, and differences in activity are only 

 some of the number of variables which enter. 



4. As stated above the temperature influences 

 practically all life phenomena in a similar characteristic 

 way, e. g., the production of C0 2 in seeds 1 and the 

 assimilation of CO a by green plants. 2 The writer 

 would not be surprised if even the aberrations in the 

 colour of butterflies under the influence of temperature 



1 Clausen, H., Landwirtschaftl. Jahrb., 1890, xix., 893. 

 » Matthaei, G. L. C, Trans. Philosoph. Soc, 1904, cxcvii., 47; Black- 

 man P. F., Ann. of Bot., 1905, xix., 281. 



