382 PHYSIOLOGY CHAP. 



Directly the blood rushes into the vacuum it froths up, owing to tthe 

 liberation of the gases. The froth collects in the upper part of the bulb, and 

 cannot pass through the minute aperture of the cock P. In order to 

 promote and complete the extraction of the gases, a cylinder of water heated 

 to about 60 C. may be applied to the exterior of A. The gases liberated 

 from the blood pass into the absorption tube B (which contains con- 

 centrated sulphuric acid in its lower end, and bits of dried pumice-stone 

 saturated with the same acid along its length) and lose their water vapour, 

 so that only dried gases reach the vessel G and are ready for chemical 

 analysis. 



The amount of blood run into the apparatus is next determined. Since 

 the total capacity of the receiver is known, the amount of water still 

 required to fill it at the end of the experiment is subtracted the difference 

 representing the volume of the blood employed. The determination is more 

 exact if the amount of water absorbed in the tube B is calculated by weighing 

 B before and after the experiment. 



For quantitative determination of the gases extracted from the given 

 amount of blood, they must be allowed to pass from the holder G into the 

 eudiometer tube K, which is filled with mercury and inverted over the 

 mercury trough /. This is easily done by making connection between G 

 and K by the tap G through H, closing the connection between G and .5, and 

 raising the vessel D by the handle L, so that G acts as a pressure -pump. 

 Frequent repetition of this process drives all the extracted gases into the 

 eudiometer. 



To determine the volume of the C0 2 , a pellet of caustic potash, moistened 

 at the surface and fused at the end to a platinum wire, is introduced into the 

 eudiometer. When all the carbonic acid is converted into potassium 

 carbonate, the pellet is removed by cautiously withdrawing the platinum 

 wire. The diminution in volume of the gas in the eudiometer gives the 

 volume of C0 2 extracted from the blood. 



The volumetric determination of the 2 is effected in a similar way 

 by introducing a pellet of phosphorus on a platinum wire, or a ball of filter- 

 paper saturated with a solution of pyrogaLLic acid in caustic potash, which 

 greedily absorbs oxygen. After the ball has been removed, the further 

 diminution of gas in the eudiometer shows the volume of 2 extracted from 

 the blood. 



The volume of gas remaining in the eudiometer after the absorption of 

 C0 2 and 2 consists of nitrogen. 



VI. Some notion of the quantity of the gases that can be 

 extracted from the blood is a necessary premiss to determining 

 the state in which they are found, whether free, or in simple 

 physical solution, or in chemical combination. 



As regards oxygen, it may be argued from the large amount 

 contained in the blood that it cannot be merely in a state of 

 solution. As a matter of fact the coefficient of absorption of 

 water for oxygen stands at a rather low figure ; at C. and 

 760 mm. Hg, of an atmosphere of pure oxygen, not more than 

 4 vols. per cent are absorbed, hence from the air (in which the 

 partial pressure of oxygen is five times less) under 1 vol. per 

 cent is absorbed. On raising the temperature of the water to that 

 of the body, the coefficient of absorption for oxygen is still further 

 lowered. It is also lowered considerably if the water is replaced 

 by a watery solution isotonic with blood plasma. Obviously, 



