300 The Influence of Environment 



phenomenon all the disturbing factors which might 

 influence the result must first be removed. When the 

 biologist works with an organism as a whole he is 

 rarely able to accomplish this since the various dis- 

 turbing influences, being inseparable from the life of 

 the organism, can often not be entirely removed. In 

 this case the biologist must look for an organism in 

 which by chance this elimination of secondary condi- 

 tions is possible. The following example may serve 

 as an illustration of this rather important point in 

 biological work. Although all normal human beings 

 have about the same temperature, yet if the heart- 

 beats of a large number of healthy human beings are 

 measured the rate is found to vary enormously. Thus 

 v. Korosy found among soldiers under the most favour- 

 able and most constant conditions of observations — 

 the soldiers were examined early in the morning before 

 rising — variations in the rate of heart-beat between 

 42 and 108. In view of this fact, those opposed to the 

 idea that the organism as a whole obeys purely physico- 

 chemical laws might find it preposterous to imagine that 

 the rate of heart-beat could be used as a thermometer. 

 Yet if we observe the influence of temperature on the 

 rate of the heart-beat of a large number of embryos of 

 the fish Fundulus, while the embryos are still in the 

 egg, we find that at the same temperature each heart 

 beats at the same rate, the deviations being only 

 slight and such as the fluctuating variations would 



