138 



ANIMAL MECHANICS. 



Professor Donders* assumes the capacity of the left ven- 

 tricle to be 188 grammes, which are equivalent to 6.63 1 oz. av., 

 ,a result which seems to me more like the capacity of both 

 ventricles, than that of one only. 



In order to find the quantity h, I shall employ the experi- 

 ments of the Rev. Dr. Hales.f Having opened a large artery, 

 such as the crural or carotid, in several animals, Dr. Hales in- 

 serted a brass or glass tube into the opening, and observed the 

 height at which the blood stood before the animal had lost 

 any large quantity of blood. The following are some of his 

 results : — » 



No. 



Artery. 



Height in Tube. 



1. 



Mare, .... 



Left Crural, . 



8. 25 feet. 



2. 



Gelding, . . 





9.66 „ 



3- 



Mare, .... 



Left Carotid, . 



9-5° „ 



4- 



Wether 



Carotid, . . . 



6' 4 6 „ 



5- 



Fallow Doe, 



Left Crural, . 



4- '7 „ 



6. 





Crural, 



6.66 „ 



An important fact was ascertained by Dr. Hales during 

 the course of these experiments, viz., that when some of the 

 blood was allowed to flow away, the force of the heart's con- 

 traction diminished, no doubt in consequence of the dimi- 

 nished resistance offered by the diminished circulation ; the 

 heart, as it were, instinctively measuring the work to be done, 

 and expending upon it exactly the force required. The height 

 of blood in the tube, which measured the force of the heart's 

 contraction, became less and less as the blood was allowed to 

 flow off, until it reached a minimum height, when the animal 

 expired. This minimum, carefully measured in the case of 

 the horses, was found to be — 



* Physiologie des Menschen (Leipzig, 1859), p. 109. 

 f Statical Essays (London, 1769), vol. ii. 



