664 



PHYSIOLOGY OF RESPIRATION. 



recirculate the air in buildings by installing proper arrangements 

 for washing it and controlling its temperature and moisture. In 

 cold weather a system of this kind reduces considerably the cost 

 of heating. 



Fig. 272. — Gas pump for extracting the gases of blood (Grehant): M and F, Mercury 

 receivers; P, windlass for raising and lowering M; to, a three-way stop-cock protected by a 

 seal of mercury or water; C, a cup with mercury over which the receiving eudiometer is 

 placed to collect the gases; B, the bulb in which, after a vacuum is made, the blood is intro- 

 duced by the graduated syringe, S. By means of the stop-cock m the vacuum in F, caused by 

 the fall of the mercury, can be placed in communication with B. After the gases have diffused 

 over into F, M is raised, and when the stop-cock m is properly turned these gases are driven 

 out through C into the receiving tube. The operation is repeated until no more gas is given 

 off from B. 



The Gases of the Blood.— The gases that are contained in the 

 blood are oxygen, carbon dioxid, and nitrogen. These gases may 

 be extracted completely and in a condition for quantitative analysis 

 by means of some form of gas-pump. The principle of most of the 

 gas-pumps used in the physiological laboratories is the same. The 



