2 THE BLOOD. 



the functions, which follows copious discharges of this fluid, life may be 

 restored by injecting into the vessels the same blood or the fresh blood of 

 another animal. This observation, which was first made on the inferior ani- 

 mals, has been applied to the human subject ; and it has been ascertained 

 that in patients sinking under hemorrhage the introduction of even a few 

 ounces of fresh blood may restore the functions for a time, and sometimes 

 permanently. 



Quantity of Blood. The determination of the entire quantity of blood 

 contained in the body has long engaged the attention of physiologists, with- 

 out, however, any absolutely definite results. The fact that physiologists 

 have not succeeded in determining definitely the entire quantity of blood 

 shows the extent of the difficulties 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 after division of the largest vessels, as after decapi- 

 tation ; and no perfectly accurate means have been devised for estimating 

 the quantity which remains. The estimates of experimenters present the 

 following wide differences : Allen-Moulins, who was one of the first to study 

 this question, estimated the quantity of blood at one twentieth the weight of 

 the entire body. The estimate of Herbst was a little higher. Hoffmann 

 estimated the quantity at one fifth the weight of the body. These observers 

 estimated the quantity remaining in the system after opening the vessels, by 

 mere conjecture. Valentin was the first to attempt to overcome this diffi- 

 culty by experiment. For this purpose he employed the following process : 

 He took first a small quantity of blood from an animal for purposes of com- 

 parison ; then he injected into the vessels a known quantity of a saline solu- 

 tion, and taking another specimen of blood some time after, he ascertained 

 by evaporation the proportion of water which it contained, and compared it 

 with the proportion in the first specimen. He reasoned that the excess of 

 water in the second specimen over the first would give the proportion of the 

 water which had been added to the whole mass of blood ; and as the entire 

 quantity of water introduced was known, the entire quantity of blood could 

 be deduced therefrom. 



The following process was employed by Lehmann and Weber, and was ap- 

 plied directly to the human subject in the cases of two decapitated criminals : 

 These observers estimated the blood remaining in the body after decapita- 

 tion, by injecting the vessels with water until it came through nearly color- 

 less. The liquid was carefully collected, evaporated to dryness, and the dry 

 residue was assumed to represent a certain quantity of blood, the proportion 

 of dry residue in a definite quantity of blood having been previously ascer- 

 tained. If it were certain that only the solid matter of the blood was thus 

 removed, such an estimate would be tolerably accurate. 



The process just described gives an idea of the probable quantity of blood 

 in the body; but the most serious objection to it is the possibility that 

 certain solid constituents of the tissues are washed out by the water passing 

 through the vessels, and it is generally thought that the estimate by Leh- 

 mann and Weber, that the quantity of blood is equal to about one eighth of 



