INFLUENCE OF TEMPERATURE UPON LIFE-PROCESSES 421 



animal and the beats counted at a variety of temperatures. The 

 following are illustrative of the results obtained by this method : 



Temperature interval. Temperature-coefficient. 



Ilto21 2.76 



15 to 25 2.24 



17 to 27 2.05 



19 to 29 2.06 



21 to 31 1.14 



at a temperature slightly above 31 the heart-beat ceases and the 

 organism dies. 



In the case of the crustacean Limulus the Heart-ganglion can be 

 heated or subjected to other manipulation without directly involving 

 th,e heart-muscle itself, and Carlson has found that by heating the 

 ganglion alone the heart-beat is accelerated, the unusually high tem- 

 perature-coefficient of 4 being obtained. 



On the other hand, in the Embryonic Heart, in which the mechanism 

 of nervous control is probably not yet established, the rate of the 

 heart-beat is similarly affected by temperature, being doubled or trebled 

 by a rise of ten degrees. The following are results obtained by Loeb 

 and Ewald, employing the embryos, still enclosed within the egg, of 

 the marine fish Fundulus: 



Time required for 19 



heart-beats in the 

 Temperature. embryo; seconds. 



30 . . '.' 6.25 



25 8.5 



20 ./.,,,; 11.5 



15 . 19.0 



10 32.5 



5 61.0 



10 33.5 



15 . ;_ 18.8 



20 12.0 



25 . '. 10.0 



30 .... . . . . , 6.0 



It is evident, therefore, that both the muscular and nervous mechan- 

 isms involved in the regulation of the rate of the heart-beat are pri- 

 marily conditioned, as to their velocity, by underlying chemical 

 transformations. 



Loeb and Ewald have drawn attention to the fact that in Fundulus 

 embryos the rate of the heart-beat is almost the same in all the embryos 

 exposed to the same temperature, provided they still remain enclosed 

 within the egg. This is because of the elimination of all secondary 

 disturbing factors. As soon as the embryos begin to move, this 

 equality disappears, because the motility of different embryos differs 

 and the products discharged from the contracting muscles influence 

 the rate of the heart-beat. In man and in other higher animals, the 

 number of the disturbing factors, while the heart remains in situ, are 

 so great that no uniformity of rate at any given temperature can be 

 expected. " Differences in emotions or the internal secretions following 



