THE BLOOD. 231 



one of them with pure water, the other with the fluid of injection, until 

 each, placed before the slit of the spectroscope, just allowed the green 

 light of the spectrum to be visible. From the relative quantities of the 

 two liquids needed to produce this result, the amount of hemoglobine, 

 and consequently of blood, extracted by the injection could be calculated. 

 This quantity, added to that which had escaped spontaneously from 

 the vessels, gave the entire amount of blood, as follows : 



QUANTITY OF BLOOD, AS COMPARED WITH THE BODILY WEIGHT. 



In I - from 8.00 to 8.93 per cent. 



" Cats. 8.40 " 9.61 



" Guinea-pigs, " 8.13 " 8.33 " 



" Rabbits. " 7.50 i; 8.13 " 



There is evidence that the quantity of blood varies in the same 

 animal, according to various bodily conditions, and especially 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. Ber- 

 nard* observed that if two animals of the same weight, one in full 

 digestion and the other fasting, be suddenly decapitated, the quantity 

 of blood discharged from the former is 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 much blood can be withdrawn without causing death, as in one of the 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 in the fasting condition. The volume of blood in the body 

 fluctuates, therefore, within certain limits, with the introduction of 

 nutritious matter by digestion and its expenditure during the interval. 



The most satisfactory determination of the quantity of blood in man 

 is that by Weber and Lehmann.f These observers operated on two 

 criminals executed by decapitation ; the methods and results being 

 essentially the same in both. In one case, the body weighed before 

 decapitation 60.14 kilogrammes; and the blood which escaped sponta- 

 neously amounted to 5540 grammes. To estimate the quantity remain- 

 ing 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 ascertained the 

 amount of its solid matter. The result Was as follows : 



Blood which escaped from the vessels . . 5540 grammes. 

 " remained in the body . . 1980 " 



Entire quantity, . . 7520 " 



The blood, accordingly, amounted during life to 12.54 per cent, of the 

 bodily weight. Bischoff, in a similar observation, in 1855, found it 

 only about 8 per cent. As in Steinberg's experiments the quantity of 

 blood in the cat also varied by 50 per cent, above the minimum, it 

 will probably be near the truth to estimate its average quantity in the 

 human subject at about 10 per cent, of the bodily weight; and a man 

 weighing 65 kilogrammes (143 pounds avoirdupois) would therefore 

 have 6500 grammes, or a little over 14 pounds of blood. 



*Lefons sur les Liquides de 1'Organisme. Paris, 1859, tome i., p. 419. 



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



