126 A MANUAL OF PHYSIOLOGY 



route. If it passes through the intestines and liver, or through the 

 kidney, or through the lower limbs, it takes a long route. So that 

 to determine the total circulation-time by direct measurement we 

 must know (i) the quantity of blood that passes on the average by 

 each path in a given time, and (2) the average circulation-time of 

 each path. If the average weight of blood in each organ be repre- 

 sented by w lt w. 2 , w 3 , etc. ; and the average circulation-times by 

 /!, t. 2 , t 3 , etc. ; and / be the total systemic circulation-time ; then 



w i~* W 2~' w -\ ' etc -' w ^ represent the quantity of blood passing 



n h *3 



through each organ in / seconds, since in the average circulation- 

 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. 



// 





ffl 



FIG. 52. TIME OF THE LESSER CIRCULATION. CAT ANESTHETIZED 

 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, circulation-time after section of both vagi (much 

 diminished) ; III, circulation-time during stimulation of the peripheral end of 

 one vagus (much increased). 



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

 passes once round the systemic circulation in t seconds. Therefore, 



tit 



w + w 2 +w~, etc.,= W. In this equation everything can be 



J| *2 , ^3 



determined oy experiment except t, and therefore t can be calculated. 

 Adding / 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 



