THE CIRCULATION OF THE BLOOD AND LYMPH 127 



from the pulmonary veins, and therefore upon the inflow into the 

 right side of the heart from the systemic veins) varies widely, some 

 of the mechanical effect of the contraction must be wasted when 

 the quantity is less than the ventricle is capable of expelling. 



Output of the Heart. If 5^ kilos of blood pass through the heart 

 in i minute with the average pulse- rate of 72 per minute, the quantity 



r COO 



ejected by either ventricle with every systole will be - = 76 grm., 



or about 72 c.c. This is much less than the amount assigned by 

 Vierordt, which has gained the greatest vogue in physiological text- 

 books, but all recent observers who have directly measured the out- 

 put are agreed that Vierordt's estimate is too high. Thus, in a series 

 of experiments on more than 20 d^gs, ranging in weight from 5 to 

 nearly 35 kilos, it has been shown that the output, or contraction 

 volume, as it is sometimes called, of the left ventricle per kilo of 

 body-weight diminishes as the size of the animal increases ; and the 

 relation between body-weight and output is such that in a man 

 weighing 70 kilos we can hardly suppose that the ventricle discharges 

 more than 105 grm. of blood per second, or 87 grm. (80 c.c.) per 

 heart-beat with a pulse-rate of 72. Putting this result along with 

 that deduced from the circulation-time, we can pretty safely conclude 

 that the average amount of blood thrown out by each ventricle at 

 each beat is not more than 70 or 80 c.c. Zuntz, from the quantity 

 of oxygen absorbed by the blood in the lungs, has estimated the 

 output at 60 c.c. But according to him this may be doubled during 

 severe muscular work, when, as a matter of fact, by the aid of the 

 X-rays or by percussion of the chest, the volume of the heart may 

 be shown to be considerably increased. In the middle of last 

 century, Passavant calculated the output at 46-5 grm., which is almost 

 certainly too low. 



The Relation of the Nervous System to the Circulation. 



So far we have been considering the circulation as a purely 

 physical problem. We have spoken of the action of the 

 heart as that of a force-pump, and perhaps to a small extent 

 that of a suction-pump too. We have spoken of the blood- 

 vessels as a system of more or less elastic tubes through 

 which the blood is propelled. We have spoken of the re- 

 sistance which the blood experiences and the pressure which 

 it exerts in this system of tubes, and we have considered 

 the causes of this resistance, the interpretation of this 

 pressure, and the physical changes in the vascular system 

 that may lead to variations of both. But so far we have 

 not at all, or only incidentally and very briefly, dealt with 



