86 CIRCULATION OF THE BLOOD 



solution, introduced into the circulation, would have a tendency to 

 diffuse itself throughout the whole mass of blood, it might be, with 

 considerable rapidity. This certainly is an element that should be 

 taken into account; but from the definite data obtained concerning 

 the rapidity of the arterial circulation and the inferences that are un- 

 avoidable in regard to the rapidity of the venous circulation, it would 

 seem that the saline solution must be carried on by the mere rapidity 

 of the arterial flow to the capillaries, which are very short, taken up 

 from them, and carried on by the veins, and thus through the entire 

 circuit, before it has had time to diffuse itself to any considerable ex- 

 tent. It is not apparent how this objection can be overcome ; for a 

 substance must be used that will mix with the blood, as otherwise it 

 could not pass through the capillaries. 



There seems no reason why, with the above restrictions, the results 

 obtained by Hering and Vierordt should not be accepted and their 

 application be made to the human subject. 



Hering found that the rapidity of the circulation in different ani- 

 mals had an inverse ratio to their size and a direct ratio to the rapidity 

 of the action of the heart. 



The following are the mean results in certain of the domestic ani- 

 mals, taking the course from jugular to jugular, when the blood passes 

 through the lungs and through the capillaries of the head : 

 



In the Horse, the circulation is accomplished in 27.3 seconds. 



In the Dog, the circulation is accomplished in 15.2 seconds. 



In the Goat, the circulation is accomplished in 12.8 seconds. 



In the Rabbit, the circulation is accomplished in 6.9 seconds. 



Applying these results to the human subject and taking into ac- 

 count the size of the body and the rapidity of the heart's action, the 

 duration of the circuit from one jugular to the other may be estimated 

 at 21.4 seconds, and the general average through the entire system, at 

 23 seconds. This estimate is simply approximate ; but the results in 

 the inferior animals may be received as nearly accurate. 



Estimates of the time required for the passage of the whole mass of 

 blood through the heart are even less definite than the estimate of the 

 general rapidity of the circulation. To arrive at a 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 the entire mass of blood is divided by the quantity discharged from 

 the heart with each ventricular systole, the result will be the number 

 of pulsations required for the passage of the blood through the heart ; 

 and knowing the number of beats per minute, the length of time thus 



