380 THE HUMAN BODY. 



This suggests that the coloring matter or lic&moglobin of 

 the red corpuscles combines with oxygen to form a scarlet 

 compound, and when deprived of that gas has a darker and 

 more purple color; and other experiments confirm this. 

 Haemoglobin combined with oxygen is known as oxylicemo- 

 globin and it is on its predominance that the color of 

 arterial blood depends. Haemoglobin uncombined with oxy- 

 gen is reduced Timmoglobin; it predominates in venous blood, 

 and is alone found in the blood of a suffocated mammal. 



The Laws Governing the Absorption of Gases by a 

 Iiiquid. 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 combine chemically with it, takes up a definite volume 

 of the gas. If the gas be compressed the liquid will still, 

 at the same temperature, take up the same volume as before, 

 but now it takes up a greater weight; and a weight exactly 

 as much greater as the pressure is greater, since one volume 

 of a gas under any pressure contains exactly twice as much 

 of the gas by weight as the same volume under half the 

 pressure; and so on. A liter or a quart of water, for example, 

 exposed to the air will dissolve a certain amount of oxygen. 

 If the air (and therefore the oxygen in it) be compressed to 

 one fourth its bulk then the water will dissolve exactly the 

 same volume of oxygen as before, but this volume of the 

 compressed gas will contain exactly four times as much 

 oxygen as did the same volume of the gas under the origi- 

 nal pressure; and if now the pressure be again diminished 

 the oxygen will be given off exactly in proportion as its 

 pressure on the surface of the water decreases. Finally, 

 when a complete vacuum is formed above the surface of the 

 water it will be found that the latter has given off all its 

 dissolved oxygen. This law, that the quantity of a gas dis- 

 solved by a liquid varies directly as the pressure of that gas 

 on the surface of the liquid is known as Dalton's law (see 

 Physicn), 



