XI 



KESriEATOEY EXCHANGES 



381 



<i i- tlieu brouglit back to its first position by a quarter turn, so that G is now 

 connected with H and no longer with A and B, while the vessel D is on<-<- 

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

 repetition of this process (of turning the tap G, 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. Pfluger's apparatus for extraction of blood gases. (Explanation in text.) 



y of the manometer 0, attached to the tube that connects C with B, 

 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-wav 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 tin- required quantity into the bulb A. 



