348 



RESPIRATION. 



connection with the receiver containing the blood, which thereupon becomes pro- 

 portionately exhausted. By again adjusting the cocks and once more elevating 

 the movable globe, the gas thus extracted is driven out of the fixed globe into 

 a receiver. The vacuum is then once more established and the operation re- 

 peated as long as gas continues to be given off from the blood. 



A modified form of pump working on the same principles as that of Ludwig, 

 but involving the use of only one globe to be made vacuous and one movable 

 reservoir for mercury, has been constructed by Pfliiger. It presents several advan- 

 tages over the one just described, the chief being that (1) non-defibrinated blood 

 may be used for the extraction of gases, (2) the vacuum into which the gases are 

 evolved is large, (3) this vacuum is kept dry by being connected laterally with a 

 vacuous chamber containing sulphuric acid. The details of this construction are, 

 however, complicated, and the greatest care is required in its use to avoid break- 



FIG. 93. 



Diagram of Alvergniat's Pump. 



age. Of later years a simplified form of pump has been introduced for laboratory 

 work. It was first used by Grehant and Paul Bert, and is now frequently called an 

 Alvergniat's pump, from the name of its present maker. Fig. 93 gives a diagram- 

 matic representation of its construction. 



A is a glass bulb some five inches in diameter, blown on to a glass tube a below 

 and on to a vertical tube b above. The lower end of a is connected by a thick- 

 walled India-rubber tube with a reservoir for mercury J?, which can be raised 

 and lowered by means of a string passing over a pulley c. The vertical tube b 

 is thickened at one place, and into this thickened portion a three-way tap d is 

 ground. The upper end of b is prolonged (above the three-way tap) into a fine 

 point. This point passes by a tight joint through the bottom of a vessel e, which 

 can be partly filled with mercury, and over which a receiver /. filled with mercury 



