CH. XXIV.] 



AIR-PUMPS. 



383 



enter into ebullition, and the gases will pass off into /'and C, and on raising 

 M and then L. the stopcock B being opened and 6 closed, the gas is driven 

 through A, and is received into the receiver over mercury. By repeating the 

 experiment several times the whole of the gases of the specimen of blood is 

 obtained, and may be estimated. 



The very simple air-pump (fag. 334) devised by Leonard Hill will be, 

 however, amply sufficient for most purposes. It consists of three glass bulbs ; 

 (B.B.), which we will call the blood bulb ; this is closed above by a piece of 

 tubing and a clip, a ; this is connected by good india-rubber tubing to another 

 bulb, d. Above d, however, there is 

 a stopcock with two ways cut through 

 it : one by means of which B.B. and 

 d may be connected, as in the figure ; 

 and another seen in section, which 

 unites d to the tube e, when the stop- 

 cock is turned through a right angle. 

 In intermediate positions, the stop- 

 cock cuts off all communication from 

 il to all parts of the apparatus above 

 it ; d is connected by tubing to a 

 receiver, R, which can be raised or 

 lowered at will. At first the whole 

 apparatus is filled with mercury, R 

 being raised. Then, a being closed, 

 R is lowered, and when it is more 

 than the height of the barometer 

 (30 inches) below the top of B.B. 

 the mercury falls and leaves the blood 

 bulb empty : by lowering R still 

 further, d can also be rendered a 

 vacuum. A few drops of mercury 

 should be left behind in B.B. B.B. is 

 then detached from the rest of the 

 apparatus and weighed, the clips, a 

 and b, being tightly closed. Blood 

 is then introduced into it by con- 

 necting the tube with the clip a on 

 it to a cannula filled with blood 

 inserted in an artery or vein of a 

 living animal. Enough blood is 

 withdrawn to fill about half of one 

 of the bulbs. This is defibrinatrd 

 by shaking it with the few drops 

 of mercury left in the bulbs. It is 

 then weighed again : the increase of 

 weight gives the amount of blood 

 which is being investigated. B.B. is 

 then once more attached to the rest 

 of the apparatus, hanging downwards, as in the side drawing in fig. 334, and 

 the blood gases boiled off ; these pass into d, which has been made a vacuum ; 

 and then, by raising R again, the mercury rises in d, pushing the gases in 

 fn.iit of it. through the tube, e (the stopcock being turned in the proper 

 direction), into the eudiometer, E, which has been filled with and placed 

 over mercury. The gas can then be measured and analysed. 



Gas analysis. There are many pieces of apparatus devised for this 

 purpose. In physiology, however. \ve liave gem-rally to deal with only three 

 oxygen, nitrogen, aed carl ionic acid. 



Waller's modification of Xuntz's more complete apparatus will be found 

 very useful in performing gas analysis, say, of the expired air. or of the blood 



Fig. 335. Waller's apparatus for pis 

 analysis. 



