CHAP. IV.] THE BLOOD. METHODS OF RESEARCH. 



197 



the actual form of mercurial pump employed and the details of the 

 different operations employed by different experimenters, and, indeed, 

 in different laboratories, vary very much. 



We shall here describe (1) methods of collecting blood intended 

 for gas analysis ; (2) the various pumps which may be employed with 

 advantage ; and (3) the methods of determining the composition of 

 the separated gases. 



Collection of Blood for the Determination of its Gases. 



In all cases the blood to be investigated must be collected over 

 mercury in such a way as to avoid all access of air. 



The apparatus (Fig. 39) is admirably adapted for this purpose 



FIG. 39. APPARATUS FOR COLLECTING BLOOD OF WHICH THE GASES ARE TO BE DETERMINED, 



