100 THE BLOOD. 



already alluded to, of transfusion of the blood of a calf into 

 the veins of a man. 



In the human subject, especially after hemorrhage, the 

 vital powers are sometimes restored by careful transfusion 

 of human blood, with the above precautions; remembering 

 that a very small quantity, three or four ounces, will some- 

 times be sufficient. 



Quantity of Blood. The determination of the entire 

 quantity of blood contained in the body is a question of great 

 interest, and has long engaged the attention of physiologists, 

 without, however, absolutely definite results. Among those 

 who have experimented on this point, may be mentioned 

 Allen-Moulins, Herbst, Fried. Hoffmann, Valentin, Blake, 

 Lehmann and Weber, and Vierordt. 1 The fact that the 

 labors of these eminent observers have been so far unsuccess- 

 ful in determining definitely the entire quantity of blood, 

 shows the difficulties which are to be overcome before the 

 question can be entirely settled. The chief difficulty lies in 

 the fact that all the blood is not discharged from the body 

 on division of the largest vessels, as after decapitation ; and 

 no perfectly accurate means have been devised for estimating 

 the quantity which must always remain in the vessels. The 

 estimates of experimenters present the following wide differ- 

 ences. Allen-Moulins, who was one of the first to study this 

 question, estimates the quantity of blood at one-twentieth 

 the weight of the entire body. The estimate of Herbst is a 

 little higher. Hoffmann estimates the quantity at one-fifth 

 the weight of the body. These observers estimated the quan- 

 tity remaining in the system after opening the vessels, by 

 mere conjecture. Yalentin was the first who attempted to 

 overcome this difficulty by experiment. For this purpose 



1 The reader is referred to the works of Longet (Physiologic, Paris, 1861, 

 tome i., p. 705 et seq.} and Milne-Edwards (Physiologie, Paris, 1857, tome i., p. 

 308 et scq.\ for a more extended account of the various experiments which have 

 been made with a view of determining the entire quantity of blood in the body. 



