320 CIRCULATION OF BLOOD. IlECT. XVII. 



method appears to me to be incapable of furnishing correct 

 results. 



Moreover, there exists another mode of experimenting, 

 which the celebrated Hales first applied to the investigation 

 of the velocity of the circulation. It is based on a princi- 

 ple essentially accurate, and consists in deducing the velocity 

 from the capacity of the ventricles, and from the number of 

 pulsations of the heart in a given time. 



Hales measured the rapacity of the left ventricle of a 

 horse, and of several other animals, by taking a cast of the 

 ventricle, by pouring melted wax into it, and allowing it 

 to solidify therein. He found, that the capacity of the left 

 ventricle of a mare was equal to 10 cubic inches ; and the 

 weight of 1 cubic inch of blood being 267'7 grains, it follows 

 that the total weight of the blood contained in the ventri- 

 cle was about 6 ounces avoirdupoise. Assuming that, at 

 each pulsation, the ventricle completely empties itself, 6 

 ounces of blood would be expelled at each contraction, 

 and seventy-two of these contractions would be necessary 

 to effect the complete circulation of the 36 pounds (troy) 

 of blood which the horse contains. His result is very dif- 

 ferent from that obtained in the experiments of Hering, 

 relative to the velocity of the circulation. For, if the heart 

 of a horse made only sixteen pulsations in twenty-five 

 seconds, there could not escape from the ventricle, in that 

 interval of time, more than 8 pounds (troy) of blood. It 

 would be difficult to account for such a very great discre- 

 pancy in these results, if we assumed Hering's numbers to 

 be correct. 



We shall here quote the numbers given by Hales for the 

 time required for the completion of the circulation in man. 



Assuming seventy-five pulsations per minute, from 24 to 

 30 pounds for the weight of the total mass of blood, and 2 

 ounces to be about the quantity thrown out at each con- 



