XI 



KESPIKATOBY EXCHANGES 



381 



G is then brought back to its first position by a quarter turn, so that C is now 

 connected with H and no longer with A and .B, while the vessel D is once 

 more raised, driving the air out of (7, which fills with mercury. Frequent 

 repetition of this process (of turning the tap 6r, alternately with raising and 

 lowering of the vessel D of the mercury pump) produces a perfect vacuum 

 throughout the apparatus, which occurs at the exact moment at which the 



FIG. 167. Pfliiger's apparatus for extraction of blood gases. (Explanation in text.) 



mercury of the manometer 0, attached to the tube that connects C with J9, 

 falls to zero. The steadiness or oscillations of the manometer column show 

 whether the apparatus is air-tight or not. 



After making a perfect vacuum, the pointed upper end of the bulb A is 

 connected with the cannula previously introduced into the blood-vessel 

 (carotid or jugular). The 2- way tap M is turned so as to fill the connecting 

 tube with blood which drives the air out, after which another quarter turn 

 of the same tap lets the blood flow in the required quantity into the bulb A. 



