106 CIRCULATION OF THE BLOOD IN THE VESSELS. 



Hering found that the rapidity of the circulation in different animals 

 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 animals, 

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

 lungs and through the capillaries of the face and head : 



In the Horse, the circulation is accomplished in 27 - 3 seconds. 



Dog, " " 15-2 " 



" Goat, " " 12-8 " 



Rabbit, " " 6-9 " 



Applying these results to the human subject and 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 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 very 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 any satisfactory result, it is neces- 

 sary to know the entire quantity of blood in the body and the exact quantity 

 which passes through the heart at each pulsation. If the whole mass of blood 

 be divided by the quantity discharged from the heart with each ventricular 

 systole, the result gives 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, the length of time thus occupied is ascertained. The objection 

 to this kind of estimate is the inaccuracy of the data respecting the quantity 

 of blood in the system as well as the quantity which passes through the heart 

 with each pulsation. Nevertheless, an estimate can be made, which, if it be 

 not entirely accurate, can not 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-tenth the weight of the body, or 

 fourteen pounds (6-35 kilos.), in a man weighing one hundred and forty 

 pounds (63-5 kilos.). The quantity discharged at each ventricular systole is 

 estimated by Valentin at five ounces (141-7 grammes), and by Volkmann, at 

 six ounces (170-1 grammes). Assuming that at each systole, the left ventricle 

 discharges all its blood, except perhaps a few drops, and that this quantity in 

 an ordinary-sized man is five ounces (141-7 grammes), it would require forty- 

 five pulsations for the passage through the heart of the entire mass of blood. 

 Assuming the pulsations to be seventy- two per minute, this would occupy 

 thirty-seven and a half seconds. 



The relation of the rapidity of the circulation to the frequency of the 

 heart's action is a question which was not neglected in the experiments of 

 Hering. It is evident that if the charge of blood sent into the arteries be the 

 same, or nearly the same, under all conditions, any increase in the number of 

 pulsations of the heart would produce a corresponding acceleration of the 

 general current of blood. This is a proposition, however, which can not be 



