158 THE WORK DONE BY THE II E ART. [BOOK i. 



that the whole contents of the ventricle are ejected at each systole. 

 Yolkmann measured the sectional area of the aorta, and taking an 

 average velocity of the blood in the aorta (a very uncertain datum), 

 calculated the quantity of blood which must pass through the sectional 

 area in a given time. The number of beats in that time then gavo 

 him the quantity flowing through the area, and consequently ejected 

 from the heart, at each beat. The mean of many experiments on 

 different animals came out '0025 p. c. of the body weight, which in. 

 a man of 75 kilos would be 187*5 grms. Yierordt measured the mean 

 velocity and the sectional area in the carotid, and thence, from a 

 measurement of the sectional area of the aorta, and from a calculation 

 of the blood's mean velocity in it, based on the supposition that the 

 mean velocity in an artery was inversely as its sectional area, arrived 

 at the quantity flowing through the aortic sectional area in a given 

 time, and thus at the quantity passing at each beat. Both these 

 calculations are vitiated by the fact that the variations of velocity 

 in the aorta are so great, that any mean has really but little positive 

 value. 



Pick by means of calculations based partly on the data gained by 

 observing the increase of the volume of the whole arm at each cardiac 

 systole, arrived at results much less than either of the above. In one 

 case he estimated the quantity ejected from the heart at each beat 

 at 53 grm., and in a second case at 77 grm. 



It must be remembered that though it is of advantage to speak 

 of an average quantity ejected at each stroke, it is more than 

 probable that that quantity may vary within very wide limits. 

 Taking, however, 180 grms. as the quantity, in man, ejected at 

 each stroke at a pressure of 250 mm. 1 of mercury, which is equiva- 

 lent to 3'21 metres of blood, this means that the left ventricle is 

 capable at its systole of lifting 180 grms. 3'21 m. high, i.e. it does 

 578 gram-metres of work at each beat. Supposing the heart to 

 beat 72 times a minute, this would give for the day's work of the 

 left ventricle, nearly 60,000 kilogram-metres ; calculating the work 

 of the right ventricle at one-fourth that of the left, the work of the 

 whole heart would amount to 75,000 kilogram-metres, which is 

 just about the amount of work done in the ascent of Snowdon by 

 a tolerably heavy man. A calculation of more practical value is 

 the following. Taking the quantity of blood as $ of the body 

 weight, the blood of a man weighing 75 kilos would be about 

 5,760 grms. If 180 grms. left the ventricle at each beat, a 

 quantity equivalent to the whole blood would pass through the 

 heart in 32 beats, i.e. in less than half a minute. 



1 A high estimate is purposely taken here. 



