RESPIRATION. 363 



from both venous and arterial blood shows that each consists of 

 oxygen, carbon dioxid, and nitrogen, though in different amounts. 

 An average composition of the gases extracted from dog's blood 

 obtained from the right ventricle and carotid artery is given in the 

 following table: 



Venous blood j Carbon dio'xid V ~" c "**"' Arteri al blood 



loovols. ( Nitrogen , .__' z _ ^ 100 vols. iNitrogen> ___ 



The changes produced in the blood by respiration, both external 

 >|ind internal, become apparent from a comparison of t these analyse s, . 

 uhe venous blood while passing through the lung's^ain^f?orrr^gnL u * > 

 to eleven volumes per cent, of oxygen and loses rive volumes per 

 cent, of carbon dioxid. ^The arterial blood while passing through 



the tissues loses oxygen and gains carbon dioxid in corresponding 

 amounts.^ The volume of nitrogen is not appreciably changed. % 



The Relation of the Gases in the Blood. The mechanism 

 by which the gases become associated with the blood at the moment 

 of their entrance into it, and again become dissociated just prior to 

 their exit from it, as well as their relation while in transit, will be more 

 readily understood after reference to a few elementary facts relative 

 to the absorption of gases in general and the conditions of temperature 

 and pressure by which it is influenced. 



It is well known that liquids will take up, absorb, or dissolve 

 unequal volumes of different gases in accordance with their solu- 

 bilities and with variations in temperature and pressure. Water, 

 for example, will absorb oxygen, carbon dioxid, and nitrogen as well 

 as other gases in amounts varying with the foregoing conditions, 

 ^he amount of any gas absorbed by one volume of a liquid at a tem- 

 perature of o C. and a pressure of 760 mm. Hg is known as the co- 

 efficient of absorption. ^The coefficient of absorption of i volume 

 of distilled water for oxygen is 0.0489 volume; of carbon dioxid, 

 1.797 volumes; of nitrogen, 0.023 volume. With a rise in tem- 

 perature, however, the absorptive power of water for each one of 

 these gases diminishes. ^On the contrary, as the pressure rises the 

 ^quantity of the gas absorbed increases, and as it falls, decreases. 1 ^ 

 \In all gaseous ^detenninatipns^^ereforey it is always necessary, for 

 purposes of ^comparison, to reducejthe orJtalne^rv^u1iies~to standard 

 temperature (o C.) and pressure mm. 'Hg)'^~~ 



If water be exposed to atmospheric air consisting of oxygen, 

 carbon dioxid, and nitrogen in the ordinary proportions, at any 

 given temperature and pressure, the -water will absorb unequal 

 volumes of each of the three gases. The pressure under which 

 each gas is absorbed is a part only, however, of the total atmos- 

 pheric pressure at the time. The pressure exerted by any one of 



