268 THE BLOOD. 



had been used for injection being then mingled, a small quantity of it 

 was taken, and the proportion of hemoglobine contained in it determined 

 by the spectroscopic test as follows : Equal quantities of pure blood were 

 placed in two similar test-tubes, and diluted, one of them with pure 

 water, the other with the fluid of injection, until each of them, placed 

 before the slit of the spectroscope, just allowed the green light of the 

 spectrum to become visible. From the relative quantities of the two 

 liquids which must be added to produce this result, the amount of 

 hemoglobine, and consequently of blood, extracted by the injection could 

 be readily calculated. This quantity, added to that which had escaped 

 spontaneously from the vessels, gave the entire amount of blood, as 

 follows : 



QUANTITY OF BLOOD, IN VARIOUS ANIMALS, AS COMPARED WITH THE WEIGHT OF THE 



WHOLE BODY. 



In Dogs, from 8.00 to 8.93 per cent. 



" Cats, " 8.40 " 9.61 



" Guinea-pigs, " 8.13 " 8.33 

 " Babbits, " 7.50 " 8.13 



There is evidence, however, that the quantity of blood varies naturally, 

 in the same animal^ according to the condition of the system at large, 

 and especially according to that of the digestive process. Steinberg 

 found that in the cat, while fasting, the percentage of blood was reduced 

 from 8.40 to 5.61 per cent. Bernard 1 has observed that if two animals 

 of the same weight, one of which is in full digestion while the other is 

 fasting, be suddenly decapitated, the quantity of blood discharged from 

 the former is much greater than that from the latter. He has also 

 shown that, in a rabbit during digestion, twice as much blood can be 

 withdrawn without causing death, as in one of the same weight but 

 in the fasting condition. The volume of the blood, therefore, contained 

 in the body, fluctuates, within certain limits, with the alternate intro- 

 duction of nutritious matter by digestion and its expenditure during 

 the interval of fasting. 



The most satisfactory determination of the quantity of blood in the 

 human subject is that by Weber and Lehmann. 2 These observers 

 operated upon two criminals who suffered death by decapitation ; the 

 methods and results being essentially the same in both cases. In one 

 of them the body weighed before decapitation 60.14 kilogrammes ; and 

 the blood which escaped from the vessels at the time of decapitation 

 amounted to 5540 grammes. In order to estimate the quantity of blood 

 which remained in the vessels, the experimenters injected the arteries 

 of the head and trunk with water until it returned from the veins of a 

 pale red or yellow color, collected the fluid thus returned, and ascer- 

 tained how much solid matter it held in solution. This, amounted to 



1 LeQons sur les Liquides de TOrganisme. Paris, 1859, tome i. p. 419. 



2 Physiological Chemistry, Cavendish edition. London, 1853, vol. ii. p. 269. 



