138 



THE CIRCULATION OF THE BLOOD AND LYMPH 



II 



JLJLJUUJLJl-JLJUUU^ 



tion-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 t seconds. Therefore, 



w. \-w 2 l-z^o , etc.,=W. In this equation everything can be de_ 



'l <2 *3 



termined by experiment except t, and therefore t can be calculated. 

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

 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 



_j | _ minute and a quarter. 



We shall see directly 

 that this estimate is 

 confirmed by data de- 

 rived from a different 

 source. In the mean- 

 time, we may use it 

 provisionally to calcu- 

 late the work done by 

 the heart. Let us take 

 for simplicity the total 

 circulation - time as i 

 minute in a 70 -kilo 

 man, the quantity of 

 blood as 4^ kilos,* and 

 the mean pressure in 

 the aorta as 150 mm. 

 of mercury. Up to the 

 time when the semi- 

 lunar valves are opened, 

 the work done by the 

 left ventricle is spent 

 in raising the intra ven- 

 tricular pressure till it 

 is sufficient to over- 

 come 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 i'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 ven- 

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



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

 tained by Haldane and Smith (p. 56). 





m 



jt jy n n n n n n n n n q_ n n n n n n n 



Fig. 62. Time of the Lesser Circulation. Cat anaes- 

 thetized with Ether. Time-trace, seconds. The line 

 above the time-trace was written by an electro- 

 magnetic signal, the circuit of which was closed at 

 the moment when injection of methylene blue into 

 the jugular vein was begun, and opened at the 

 moment when the change of colour in the carotid 

 was observed. I, normal circulation -time ; II, cir- 

 culation-time after section of both vagi (much 

 diminished); III, circulation-time during stimulation 

 of the peripheral end of one vagus (much increased). 



