THE CIRCULATION OF THE BLOOD AND LYMPH 127 



shall see directly that this estimate is confirmed by data derived from 

 a different source. In the meantime, we may use it provisionally to 

 calculate the work done by the heart. Let us take for simplicity the 

 total circulation-time as i minute in a yo-kilo man, the quantity of 

 blood as 4 1- kilos,* and the mean pressure in the aorta as 150 mm. 

 of mercury. Up to the time when the semilunar valves are opened, 

 the work done by the left ventricle is spent in raising the intra- 

 ventricular pressure till it is sufficient to overcome the pressure in 

 the aorta. If a vertical tube were connected with the left ventricle, 

 the blood would rise till the column was of the same weight as a 

 column of mercury of equal section and 150 mm. high. This column 

 of blood would be about 1-92 metres in height. If a reservoir were 

 placed in communication with the tube at this height, a quantity of 

 blood equal to that ejected from the ventricle would at each systole 

 pass into the reservoir ; and the work which the blood thus collected 

 would be capable of doing, if it were allowed to fall to the level of 

 the heart, would be equal to the work expended by the heart in 

 forcing it up. Thus, in i minute the work of the left ventricle would 

 be equal to that done in raising 4^ kilos of blood to a height of 

 i'92 metres that is, about 8*64 kilogramme-metres ; in 24 hours it 

 would be, say, 12,450 kilogramme-metres. Taking the mean pressure 

 in the pulmonary artery at one-third of the aortic pressure, we get 

 for the daily work of the right ventricle about 4,150 kilogramme- 

 metres. The work of the two ventricles is thus about 16,600 

 kilogramme-metres, t which is enough to raise a weight of nearly 

 4 pounds from the bottom of the deepest mine in the world to the 

 top of its highest mountain, or to raise the man himself to i times 

 the height of the spire of Strasburg Cathedral, or twice the height 

 of the loftiest ' skyscraper ' in New York. By friction in the 

 bloodvessels this work is almost all changed into its equivalent 

 of heat, nearly 40 calories (p. 584). Further, since the contraction 

 of the heart is always maximal (p. 141), and there is reason 

 to believe that the quantity of blood ejected at a single systole 

 by the left ventricle (being dependent upon the inflow from the pul- 

 monary 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 4^ kilos of blood pass through the heart 

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



ejected by either ventricle with every systole will be ~_ = 62'5 grm., 



or a little less than 60 c.c. This is much less than the amount 

 assigned by Vierordt, which at one time gained great vogue in physio- 

 logical text-books, but all recent observers who have directly 

 measured the output are agreed that Vierordt 's estimate is too high. 

 Thus, in a series of experiments on more than twenty dogs, 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 in- 

 creases ; and the relation between body-weight and output is such 

 that in a man weighing 70 kilos we can hardly suppose that the 



* The mean of the 5^ kilos given by most writers, and of the 3* kilos 

 obtained by Haldane and Smith (p. 49). 



f Since the blood on expulsion is moving with a certain velocity, an 

 addition might be made for its kinetic energy. But this would "only 

 increase the total work by a small fraction (about i per cent.). 



