GENERAL RAPIDITY. 347 



Applying these results to the human subject, taking 

 into account the size of the body and the rapidity of the 

 heart's action, the duration of the circuit from one jugular 

 to the other is estimated at 21*4 seconds, and the general 

 average through the entire system at 23 seconds. This is 

 simply approximative ; but the results in the inferior ani- 

 mals may be received as very nearly, if not entirely, 

 accurate. 



An estimate of the time required for the passage of the 

 whole mass of blood through the heart is even less definite 

 than the estimate of the general rapidity of the circulation. 

 To arrive at any satisfactory result, it is necessary to know the 

 entire quantity of blood in the body, and the exact quantity 

 which passes through the heart at each pulsation. If we 

 divide the whole mass of blood by the quantity discharged 

 from the heart with each systole of the ventricles, we ascer- 

 tain the number of pulsations required for the passage of the 

 whole mass of blood through the heart ; and, knowing the 

 number of beats per minute, can ascertain the length of time 

 thus occupied. 



The objection to this kind of estimate is the inaccuracy 

 of the data respecting the quantity of blood in the system, 

 and the quantity which passes through the heart with each 

 pulsation. Nevertheless, an estimate can be made, which, 

 if it be not entirely accurate, cannot be very far from the 

 truth. 



The entire quantity of blood, according to estimates 

 which seem to be based on the most reliable data, is about 

 one-eighth the weight of the body, or eighteen pounds in a 

 man weighing one hundred and forty-five. The quantity 

 discharged at each ventricular systole is estimated by Valen- 

 tin at five ounces, and by Yolkmann at six ounces. 1 In 



to be 28'8 seconds. In experimenting on the crural vein, this observer found 

 that the circulation in the lower extremities, probably from the greater length of 

 the' vessels, occupied from one to three seconds more than in the head. 



1 TODD and BOWMAN, Physiological Anatomy, American edition, 1857, p. 704. 



