688 SPECIAL PHYSIOLOGY. 



these aqueous solutions are then mixed together and measured, and the 

 tint of the mixture is compared with the standard solutions, and thus 

 the quantity of blood in it is determined. In this way, the proportion 

 of blood to the body, in the dog, is estimated at about 1 to 12. 



The quantity of blood in the body has been calculated by Vierordt, 

 by multiplying the quantity supposed to be expelled from the left ven- 

 tricle at each systole, by the number of times the heart contracts during 

 a complete circulation* of the blood through the system. The mode in 

 which the latter datum is obtained, has already been explained (p. 685 

 6) ; the former is thus arrived at. The average velocity of the blood 

 in the human carotid artery is assumed to be equal to that in the carotid 

 of a dog, and the sectional area of the vessel being known, it is easy 

 to determine by multiplying one into the other, the quantity of blood 

 which passes through any part of that artery in a second. Thus 261 

 millimetres, the velocity of the current in the carotid per second, X 

 .63 square centimetres, the sectional area of that vessel, = 16.4 cubic 

 centimetres, the quantity which passes through a certain part of the 

 vessel in one second. The quantities passing per second, in the innom- 

 inate, left subclavian, arch of the aorta, and coronary arteries of the 

 heart, are then estimated in the same way, the rate of motion of the 

 blood in the aorta being assumed to be Jth faster than it is in the carotid. 

 By these steps, Vierordt arrives at the conclusion that the quantity of 

 blood projected through the orifice of the aorta from the left ventricle, 

 every second, is 207 cubic centimetres, or 219 grammes in weight, or 

 nearly 7f oz. av. But as the heart beats 72 times in a minute or 60 

 seconds, there occur l^th systoles in each second of time; hence, the 

 quantity of blood thrown into the aorta at each systole, is about 180 

 grammes, or rather more than 6.3 oz. (p. 651). 



As all the blood in the body must pass once through the aorta in 

 every complete circulation of that fluid, and as this requires 27.7 sys- 

 toles to accomplish it, the quantity thrown at each systole, or 180 

 grammes, x 27.7, the number of heart's beats, gives for the total quan- 

 tity of blood in the body, 4986, or, in round numbers, 5000 grammes, 

 which are equal to about 11 Ibs. av. ; this, compared with the average 

 weight of the body, taken by Vierordt at 140 Ibs., is about as 1 to 

 12.6. The proportion finally adopted by Vierordt, as prevailing 

 throughout the warm-blooded Vertebrata is 1 to 13. Assuming the 

 average weight of the adult male to be 150 Ibs., the usual estimate of 

 English writers, the total quantity of blood in the body would be about 

 11 J Ibs. av. It has been found that on bleeding an animal soon after 

 feeding, nearly double the quantity of blood is obtained, as compared 

 with the result of bleeding a similarly sized animal in a state of fasting. 

 This circumstance may partly explain the great differences in the esti- 

 mates above recorded ; it also justifies the conclusion that, in certain 

 conditions of the body, the quantity of blood in the human adult of 

 average weight, may be even as much as 14 Ibs. 



The quantity of blood thrown into the aorta at each systole, which 

 is likewise the measure of the capacity of the left ventricle, is equal to 

 about ^Jflth part of the weight of the body. It would further seem 

 that, in warm-blooded animals generally, the quantity of blood flowing 



