418 THE HUMAN BODY 



oxygen, sometimes named reduced hemoglobin, predominates in 

 venous blood, and is the only kind found in the blood of a suffo- 

 cated mammal. 



The Laws Governing the Absorption of Gases by a Liquid. In 

 order to understand the condition of the gases in the blood liquid 

 it is necessary to recall the general laws in accordance with which 

 liquids absorb gases. They are as follows : 



1. A given volume of a liquid at a definite temperature if it 

 absorbs any of a gas to which it is exposed, and yet does not com- 

 bine chemically with it, takes up an amount of the gas which de- 

 pends upon two things: (1) the solubility of the gas in the liquid; 

 and (2) the pressure of the gas upon the surface of the liquid. As 

 the pressure of the gas is increased the amount of it which goes in 

 solution in the liquid is increased in exactly the same proportion. 

 If a complete vacuum be formed above a liquid all the gas con- 

 tained within it is given off. This law, that the quantity of a gas 

 dissolved by a liquid varies directly as the pressure of that gas on 

 the surface of the liquid is known as Henry's law. 



2. The amount of a gas dissolved by a liquid depends, not on 

 the total pressure exerted by all the gases pressing on its surface, 

 but on the fraction of the total pressure which is exerted by the 

 particular gas in question. For example, the average atmospheric 

 pressure is equal to that of a column of mercury 760 mm. (30 

 inches) high. But 100 volumes of air contain approximately 80 

 volumes of nitrogen and 20 of oxygen; therefore of the total 

 pressure is due to oxygen and | to nitrogen: and the amount of 

 oxygen absorbed by water is just the same as if all the nitrogen 

 were removed from the air and its- total pressure therefore reduced 

 to J of 760 mm. (30 inches) of mercury; that is, to 152 mm. (6 

 inches) of mercury pressure. It is only the fraction of the total 

 pressure exerted by the oxygen itself which affects the quantity of 

 oxygen absorbed by water at any given temperature. So, too, of 

 all the atmospheric pressure f is due to nitrogen, and all the 

 oxygen might be removed from the air without affecting the quan- 

 tity of nitrogen which would be absorbed from it by a given volume 

 of water. The atmospheric pressure would then be f of 760 mm. 

 of mercury, or 608 mm. (24 inches), but it would all be due to 

 nitrogen gas and be exactly equal to the fraction of the total 

 pressure due to that gas before the oxygen was removed from the 



