382 



RESPIRATION. 



[CH. xxiv. 



The Mercurial Air-Pump. 



The extraction of the gases from the blood is accomplished by means of 

 a mercurial air-pump, of which there are many varieties, those of Ludwig, 

 Alvergniat, Geissler, and Sprengel being the chief. The principle of action 

 in all is the same. Ludwig's pump, which may be taken as a type, is repre- 

 sented in fig. 333. It consists of two fixed glass globes, C and F, the 



upper one communicating by means 

 of the stopcock, D, and a stout india- 

 rubber tube with another glass globe, L, 

 which can be raised or lowered by means 

 of a pulley ; it also communicates by 

 means of a stopcock, , and a bent glass 

 tube, A, with a gas receiver (not repre- 

 sented in the figure) ; A dips into a bowl 

 of mercury, so that the gas may be re- 

 ceived over mercury. The lower globe, 

 F, communicates with C by means of the 

 stopcock, jK, with I in which the blood 

 is contained by the stopcock, G, and with 



3.B. 



Fig. 333. Ludwig's mercurial pump. 



Fig. 334. L. Hill's air-pump. 



a movable glass globe, M, similar to Z, by means of the stopcock. If, and the 

 stout india-rubber tube, K. 



In order to work the pump, L and M are filled with mercuiy, the blood 

 from which the gases are to be extracted is placed in the bulb J, the 

 stopcocks, H, E. D, and , being open, and G closed. M is raised by means 

 of the pulley until F is full of mercury, and the air is driven out. E is then 

 closed, and L is raised so that C becomes full of mercury, and the air is 

 driven off. B is then closed. On lowering L the mercury runs into it from 

 6', and a vacuum is established in C, On opening E and lowering .17, a 

 vacuum is similarly established in F ; it G is now opened, the blood in I will 



