

QUANTITY OF BLOOD 15 



the functions, which follows copious discharges of this liquid, life may 

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

 from another animal of the same species. This observation, which was 

 first made on the inferior animals, has been applied to the human sub- 

 ject; and it has been ascertained that in patients sinking under hemor- 

 rhage, the introduction even of 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 physiolo- 

 gists, without, however, absolutely definite results. This fact shows the 

 extent of the obstacles to be overcome before the question can be 

 absolutely settled. The chief difficulty is that all the blood is not dis- 

 charged from the body, even after division of the great arteries, as 

 after decapitation, and no entirely accurate means have been devised 

 for estimating the quantity that remains in the vessels. A process 

 devised by Haldane and Lorrain Smith is open, perhaps, to as few 

 serious objections as any. This method takes account of the hemoglo- 

 bin, a constant constituent of the red blood-corpuscles. Hemoglobin 

 combines with carbon monoxide in definite proportions, which are about 

 equal to the oxygen capacity of the blood-corpuscles. A man is made to 

 breathe a measured volume of this gas, and the percentage saturation is 

 determined. From this it is easy to calculate the proportion of carbon 

 monoxide which would be required to saturate the hemoglobin contained 

 in the entire mass of blood. It remains only to estimate the quantity of 

 carbon monoxide absorbed, and then it is not difficult to calculate the 

 quantity of this gas that would be required to saturate the entire mass of 

 blood. Such calculations have resulted, from observations on fourteen 

 healthy persons, in the estimate that the entire mass of blood is equal to 

 about one-twentieth part of the weight of the body, which is much less 

 than estimates previously made. 



Prolonged abstinence from food has a notable effect in diminishing 

 the quantity of blood, except when large quantities of liquids have been 

 taken ; and the reverse is true after the ingestion of food and drink in 

 abundance. The quantity of blood, also, is notably large in persons of 

 plethoric habit. Wrisberg reported the case of a female criminal from 

 whom nearly twenty-one and a half pounds (9745 grams) of blood flowed 

 after decapitation. It is not possible to form a definite idea of the 

 quantity of blood during digestion, but it must be considerably greater 

 than in a fasting condition. The percentage of blood that can be drawn 

 from the body without producing death varies greatly. A withdrawal 

 of twenty per cent usually is tolerated ; but a loss of thirty per cent is 

 almost invariably fatal. 



