GENERAL RAPIDITY. 349 



stances, any increase in the number of pulsations of the heart 

 would produce a corresponding acceleration of the general 

 current of blood. But this is a proposition which cannot be 

 taken for granted ; and there are many facts which favor 

 a contrary opinion. It may be enunciated as a general rule, 

 that when the acts of the heart increase in frequency, they 

 diminish in force ; which renders it probable that the ven- 

 tricle is most completely distended and emptied when its ac- 

 tion is moderately slow. When, however, the pulse is very 

 much accelerated, the increased number of pulsations of the 

 heart might be sufficient to overbalance the diminished force 

 of each act, and increase the rapidity of the circulation. 



Hering has settled these questions experimentally. His 

 observations were made on horses by increasing the frequen- 

 cy of the pulse, on the one hand, physiologically, by exercise, 

 and on the other hand, pathologically, by inducing inflamma- 

 tory action. He found, in the first instance, that in a horse, with 

 the heart beating at the rate of 36 per minute, with 8 respi- 

 ratory acts, ferro-cyanide of potassium injected into the jugu- 

 lar appeared in the vessel on the opposite side after an inter- 

 val of from 20 to 25 seconds. By exercise, the number of 

 pulsations was raised to 100 per minute, and the rapidity 

 of the circulation was from 15 to 20 seconds. The observa- 

 tions were made with an interval of 24 hours. The same 

 results were obtained in other experiments. 1 Here there is 

 a considerable increase in the rapidity of the circulation fol- 

 lowing a physiological increase in the number of beats of the 

 heart ; but the value of each beat is materially diminished ; 

 otherwise the rapidity of the current would be increased 

 about three times, as the pulse became three times as frequent. 

 In its tranquil action, with the pulse at 36, the heart con- 

 tracted thirteen times during one circuit of blood ; while it 

 required twenty-nine pulsations to send the blood over the 

 same course, after exercise, with the pulse at 100 ; showing a 



MILNE-EDWARDS, Lemons sur la Physiologic, tome iv., p. 371, note. 



