CAPACITY OF THE HEART. 137 



amount of force either the auricles or the ventricles dilate ; 

 but there is no evidence for the opinion, that in their dilata- 

 tion they can materially assist the circulation by any such 

 action as that of a sucking-pump, or a caoutchouc bag, in 

 drawing blood into their cavities. That the force which 

 the ventricles exercise in dilatation is very slight, has been 

 proved by Oesterreicher. He removed the heart of a 

 frog from the body, and laid upon it a substance suffi- 

 ciently heavy to press it flat, and yet so small as not to 

 conceal the heart from view ; he then observed that during 

 the contraction of the heart, the weight was raised ; but 

 that during its dilatation, the heart remained flat. And 

 the same was shown by Dr. Clendinning, who, applying the 

 points of a pair of spring callipers to the heart of a live 

 ass, found that their points were separated as often as the 

 heart swelled up in the contraction of the ventricles, but 

 approached each other by the force of the spring when the 

 ventricles dilated. Seeing how slight the force exerted in 

 the dilatation of the ventricles is, it has been supposed 

 that they are only dilated by the pressure of the blood 

 impelled from the auricles ; but that both ventricles and 

 auricles dilate spontaneously is proved by their continuing 

 their successive contractions and dilatations when the heart 

 is removed, or even when they are separated from one 

 another, and when therefore no such force as the pressure 

 of blood can be excercised to dilate them. By such spon- 

 taneous dilatation they at least offer no resistance to the 

 influx of blood, and save the force which would otherwise 

 be required to dilate them. 



The capacity of the two ventricles is probably exactly the 

 same. It is difficult to determine with certainty how much 

 this may be ; but, taking the mean of various estimates, 

 it may be inferred that each ventricle is able to contain 

 on an average, about three ounces of blood, the whole of 

 which is impelled into their respective arteries at each 

 contraction. The capacity of the auricles is rather less 



