CHAPTER XIV. 



DETERMINATION OF THE GASES OF BLOOD BY THE 

 PUMP METHOD. 



When blood is repeatedly exposed to a vacuum all of its gases are 

 evolved. The evolved gases can then be transferred to a suitable 

 burette and their nature and relative amounts determined. The 

 gas cannot be completely removed by one exposure of the blood 

 in a vacuum, because in such a case the gas would be evolved only 

 until equilibrium had become established between the partial 

 pressure produced by the evolved gas, and that still present in 

 the blood. It is necessary to repeat the evacuation several times. 

 For this purpose a mercury pump is usually employed, but satis- 

 factory evacuation can also be brought about by using the simpler 

 apparatus described in the following experiment. 



Experiment 51. Place about 15 c.c. defibrinated ox blood in 

 a 500 c.c. flask, and fill the latter with alveolar air by expiring 

 deeply into it through a piece of wide-bore rubber tubing, or better, 

 through a glass tube which is connected in its course with a bottle 

 filled with glass beads. This condenses and removes the water from 

 the air. Rotate the flask, so that the blood forms a thin film on the 

 walls, but do not shake in such a manner as to cause the blood to 

 froth. While rotating, occasionally expire through the tube into 

 the flask so as to maintain the percentage of carbon dioxide con- 

 stant. Continue this procedure for about three minutes, and then 

 close the flask. By this means the blood absorbs oxygen to full 

 saturation, and carbon dioxide to the same extent as the blood in 

 the pulmonary capillaries. 



Meanwhile the bulb of the blood receiver (Fig. 34A) is partially 

 evacuated by connecting it, by means of the attached piece of 

 rubber tubing, to a (water) vacuum pump. The screw clip (1) is 

 then tightened (leaving as long a piece of tubing beyond the clip 



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