RESPIRATION. 



421 



tracted from the receiver, until finally a vacuum is produced. In a similar 

 way, when the receiver connected with the pump at Z contains any gas which 

 we wish to analyze — as, for example, the gases given off by the blood in a 

 vacuum — we put a eudiometer (Eu) over the bend of the tube at P, which, of 

 course, is always under the mercury, and collect the gases as they are forced out. 



" The extraction of the last traces of gas by raising and lowering Bb is a 

 very tedious and laborious process, so that the final extraction of the gases can 

 best be accomplished by the Sprengel pump. IJKLMNHOP. The bulb and stop- 

 cock UK are made separate, as shown in the figure, and are connected with 

 LMN by a piece of rubber tubing, the whole being under mercury. This is 

 accomplished by the bend JKLM, which is made so as to allow a narrow wooden 

 box filled with the mercury to be slipped up over the bend high enough to 

 cover the stopcock and thus prevent leakage of air. The same arrangement is 

 shown at X, and is indicated by a dotted line in each instance. When the 

 stopcock K is opened the mercury flows in, drops down the tube NHOP, and 

 extracts the gases at H in the well-known manner of the Sprengel pump. The 

 large bulb is for rapid exhaustion down to the last few millimeters of pressure, 

 the rest being accomplished more slowly but more perfectly by the Sprengel. 

 In extracting blood-gases the oxygen is given off suddenly and the C0 2 slowly. 

 The great desideratum is to keep the tension of the gases in the blood-chamber 

 down as near zero as possible — certainly below 20 millimeters of Hg. This 

 is readily done with the large bulb when the O is evolved, while the Sprengel 

 is able to remove the C0 2 as it is given off, thus obviating the continued rais- 

 ing and lowering of the reservoir bulb." 



The gases collected are driven through the tube P into a 

 eudiometer previously filled with mercury and inverted. 

 The eudiometer (Fig. 75) is a calibrated tube in which the 

 gases are measured. In the upper part of it are two plati- 

 num wires by means of which an electric spark is brought 

 in contact with the gases. Hydrogen is introduced into the 

 eudiometer in definite quantity (more than sufficient to com- 

 bine with all of the O to form H 2 ()), and a spark is gen- 

 erated between the ends of the platinum wires, causing the 

 Oandthe II to combine. The diminution in volume is now 

 noted, one-third of which diminution is equal to the total 

 volume of O obtained from the sample of blood. The quan- 

 tity of CO a may be estimated by introducing into the eudi- 

 ometer a piece of moistened fused potassium hydrate, which 

 absorbs the C() 2 , forming potassium carbonate. The loss in 

 volume is the volume of C0 2 obtained from the blood. The 

 residual gas consists of X and II, the latter being the excess 

 not combined with (). The total quantity of II introduced Fiq. 75.-Eudiometer. 

 being known, and also the quantity which combined with 

 (), the difference is deducted from the volume N and II, the remainder being 

 the volume N. Accurate analysis necessitates correction- for temperature, for 



> I! , 



