RAPIDITY OF THE CIRCULATION 87 



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 pulsa- 

 tion. Nevertheless, an estimate can be made, which, if not entirely 

 accurate, can not be far from the truth. 



The entire quantity of blood, according to estimates based on the 

 most reliable data, is about one-twentieth the weight of the body, or 

 seven pounds (3.7 kilograms), in a man weighing one hundred and forty 

 pounds (63.5 kilograms). The quantity discharged at each ventricular 

 systole is estimated at three ounces (90 cubic centimeters). It would 

 require, therefore, 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 a little more than thirty-one 

 seconds. 



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

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

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

 is the same, or nearly the same, under all conditions, an increase in the 

 number of pulsations of the heart would produce a corresponding accel- 

 eration of the general current of blood. This is a proposition, how- 

 ever, which can not be taken for granted ; and there are many facts 

 that favor a contrary opinion. It may be stated as a general rule, 

 that when the acts of the heart increase in frequency they diminish in 

 force; and this renders it probable that the ventricle is most com- 

 pletely distended and emptied when its action is moderately slow. 

 When, however, the pulse is much accelerated, the increased number 

 of pulsations of the heart might be sufficient to overbalance the di- 

 minished force of each act and would increase the rapidity of the cir- 

 culation. In regard to the relations between the rapidity of the heart's 

 action and the general rapidity of the circulation, the following con- 

 clusions may be accepted as the results of experimental inquiry : - 



1. In physiological increase in the number of beats of the heart, as 

 the result of exercise, for example, the general circulation is somewhat 

 increased in rapidity, though not in proportion to the increase in the 

 rapidity of the pulse. 



2. In pathological acceleration of the heart's action, as in febrile 

 conditions, the rapidity of the general circulation usually is diminished, 

 it may be to a considerable extent. 



3. Whenever the number of beats of the heart is considerably in- 

 creased from any cause, the quantity of blood discharged at each ven- 

 tricular systole is much diminished, either from lack of complete distention 

 or from imperfect emptying of the cavities. 



