THE DURATION OF THE CIRCULATION. 177 



through the cross-section of these vessels is (1 + 2 + 3 + 4) 207 2 cu cm As 

 the left ventricle must furnish this quantity of blood in a second, and as, in addition 

 one and one-fifth of the systole corresponds to i second, the quantity of blood 



thrown into the aorta at each systole must be 172 cu. cm., or 180 grams of blood 



which is the capacity of the left ventricle. 



THE DURATION OF THE CIRCULATION. 



The question as to the time required by the blood to make the entire circuit 

 of the circulation was first investigated by Edward Hering, in 1829, in horses by 

 injecting a solution of potassium ferrocyanid into the external jugular vein and 

 noting the time when this substance first appeared in blood withdrawn from the 

 corresponding vein on the opposite side of the neck. Carl Vierordt, in 1858, per- 

 fected the technic of these experiments by having a number of cups on a rotating 

 disc pass at uniform intervals beneath the opened vein on the opposite side of 

 the body. The first appearance of the 2 per cent, solution of potassium ferro- 

 cyanid is recognized by adding ferric chlorid to the serum separated from the 

 specimen of blood and the development of a Prussian-blue reaction. The duration 

 of the circulation was found to be as follows: 



In the horse 31.5 sec. In the goose 10.89 se c. 



dog 16.7 ' duck 10.64 " 



rabbit 7.79 " buzzard 6.73 " 



hedge-hog 7.61" " cock e 17 " 



cat 6.69 " 



A comparison of these values with the normal pulse-frequency of 

 the same animals yields the following laws: 



1. The average duration of the circulation corresponds with 27 con- 

 tractions of the heart. Applying this figure to man, the duration of 

 the circulation is 22.5 seconds, with 72 pulse-beats in the minute. 



If, therefore, the entire quantity of blood passes through the heart in 22.5 

 seconds, ^ of the entire quantity must pass through in i second. This quantity 

 is designated the second-volume of the circulation. The latter multiplied by 60 

 gives the minute-volume, and as there are 72 heart-beats in the minute, the minute- 

 volume divided by 72 represents the amount of blood propelled at each beat of 

 the heart, that is, the pulse-volume of the ventricles. The last calculations, how- 

 ever, are exposed to serious sources of error. 



2. In general the mean duration of the circulation in two species 

 of warm-blooded animals is inversely proportional to the pulse-fre- 

 quency. 



Of the influences that affect the duration of the circulation there may be 

 mentioned: 



1. A greater length of the vascular channel (for example, from the metatarsal 

 vein of one foot to that of the other) requires a longer time than a shorter channel. 

 This excess in time may be equivalent to about 10 per cent, of the diameter of 

 the circulation. 



2. Young animals, with shorter vascular channels and greater pulse-frequency, 

 have a shorter circulation-time than old animals. 



3. Rapid and effective contractions of the heart, as during muscular exertion, 

 shorten the time. On the other hand, rapid but ineffective contractions (as after 

 division of both vagi) , and slow but correspondingly larger contractions (as with 

 slight irritation of the vagus) , appear to have scarcely any effect. 



Carl Vierordt has, further, attempted to determine the quantity of blood in 

 man from his investigations in the following manner: In all warm-blooded animals 

 the circulation is completed by 27 contractions of the heart; hence, the entire 

 quantity of blood must be equal to 27 times the ventricular capacity; therefore, in 

 man, 27 times 187.5 grams, or 5062.5 grams. This quantity of blood, estimated 

 as T V of the body-weight, would correspond to a body-weight of 65.8 kilos. 



In 1879 Landois called attention to the fact that potassium ferrocyanid, being 

 a neutral potassium-salt, is a heart-poison, which, in small doses, accelerates, and 

 in large doses paralyzes, the heart. These experiments, in the course of which 



