126 A MANUAL OF PHYSIOLOGY 



time of an organ the whole of the blood in it at the beginning of 

 the period of observation will have been exchanged for fresh blood. 

 But the whole of the blood in the body, which we may call 

 W, passes once round the systemic circulation in / seconds. There- 

 fore, 7/j- + o/ 2 - 4- / 8 - etc., = W, In this equation everything can be 



*\ *2 ' ^3 



determined by experiment except /, and therefore t can be calculated. 

 Adding t to the pulmonary circulation-time, we arrive at the total 

 circulation-time. 



Although our experimental data are as yet too meagre to make the 

 calculation more than a rough approximation, it appears probable 

 that in certain animals the total circulation-time is five or six times 

 as great as the pulmonary circulation-time. If the same ratio holds 

 good in man, the total circulation-time is unlikely to be much less 

 than a minute or much greater than a minute and a quarter. We 

 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 5 \ kilos, and the mean pressure in the aorta as 200 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 200 mm. high. This column 

 of blood would be about 2 56 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 5 J kilos of blood to a height of 

 2-56 metres that is, about 14 kilogramme-metres; in 24 hours it 

 would be, say, 20,000 kilogramme-metres. Taking the mean pressure 

 in the pulmonary artery at one-third of the aortic pressure (the 

 estimates of different observers vary from one-third to one-sixth in 

 different animals), we get for the daily work of the right ventricle 

 about 7,000 kilogramme-metres. The work of the two ventricles is 

 thus about 27,000 kilogramme-metres, which is enough to raise a 

 weight of half a stone from the bottom of the deepest mine in the 

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

 to more than twice the height of the spire of Strasburg Cathedral. 

 By friction in the bloodvessels this work is almost all changed into 

 its equivalent of heat, namely, about 63,000 small calories (p. 493). 

 Further, since the contraction of the heart is always maximal (p. 131), 

 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 



