112 CIRCULATION OF THE BLOOD. 



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 hi 27'3 seconds. 

 " Dog, " 15-2 " 



" Goat, " " 12-8 " 



" Rabbit, " " 6'9 " 



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 may be 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. 



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 circula- 

 tion. 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 pulsa- 

 tion. If we divide the whole mass of blood by the quantity discharged from the heart 

 with each ventricular systole, we ascertain 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, we 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 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, 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-four. The quantity discharged at each ventricular 

 systole is estimated by Valentin at five ounces, and by Volkmann, at six ounces. In 

 treating of the capacity of the different cavities of the heart, it has been noted that the 

 left ventricle, when fully distended, contains from five to seven ounces. 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 (for in the estimates of 

 Robin and Hiffelsheim, the cavities were fully distended, and contained more than under 

 the ordinary conditions of the circulation), it would require fifty-eight 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 about forty-eight seconds. 



The almost instantaneous action of certain poisons, which must act through the blood, 

 confirms our ideas with regard to the rapidity of the circulation. The intervals between 

 the introduction of some agents, strychnine for example, into the circulation, and the 

 characteristic effects on the system, have been carefully noted by Blake, whose observa- 

 tions coincide pretty closely in their results with the experiments of Hering. 



The relation of the rapidity of the circulation to the frequency of the heart's action is 

 a question of considerable interest, 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 circumstances, any increase in the number of pulsations of the heart would 

 produce a corresponding acceleration of the general current of blood. But this is a propo- 

 sition which cannot be taken for granted ; and there are many facts which favor a con- 

 trary opinion. It may be enunciated as a general rule that when the acts of the heart 

 increase in frequency they diminish in force ; which renders it probable that the ventricle 1 

 is most completely distended and emptied when its action is moderately slow. When, 

 however, the pulse is very much accelerated, the increased number of pulsations of the 

 heart might be sufficient to overbalance the diminished force of each act and would thus 



