98 



PHYSIOLOGY 



CHAP. 



V. The estimation of the total quantity of the blood, or its 

 relations with the weight of the animal, presents great practical 

 difficulties. The older anatomists held very exaggerated views 

 on the quantity of blood in man, estimating it erroneously by the 

 amount of injection mass that can be forced into the blood-vessels 

 of a dead body. Far too low values, on the other hand, were 

 obtained at a later period by the method of completely bleeding 

 the animal (Herbst, 1822), since this does not sufficiently take 

 into account the quantity of blood left in the vessels, which may 

 vary considerably in different cases. 



FIG. 25. Hedin's small centrifuge. By means of three cogged wheels enclosed within 1, -2, 3, each 

 turn of the handle is multiplied 100 times from the axis A, the apex of which carries a cross- 

 piece, with the test-tube holders pp, which are kept horizontal during the rotation. 



A better method is that carried out by Lehinann and Ed. 

 Weber on two criminals (1853). They weighed the individuals 

 before and after decapitation, and from the difference in weight 

 estimated the mass of blood lost by bleeding. They took a sample 

 of this blood. They then injected water through the arteries of 

 the trunk and head, until it flowed almost colourless from the 

 veins, and lastly determined the weight of the solids contained 

 in the blood and in the washings. From these determinations 

 they calculated the quantity of blood left in the body after 

 decapitation. 



It is obvious that this method must give too high a result. 

 The introduction of water into the vessels must extract not only 



