ESTIMATION OF THE BLOOD-GASES. 55 



35. Quantitative Estimation of the Blood-Gases. 



The gases obtained from blood consist of 0, C0 2 and N. Pfliiger 

 obtained (at 0C. and 1 metre Hg pressure), 47'3 volumes per cent, 

 consisting of 



O 16'9 per cent. - CO., 29 per cent. - N. 1'4 per cent. 

 As is shown in Fig. 15, the gases are obtained in an eudiometer, 

 i.e., in a narrow tube, J, closed at one end, and with a very exact scale 

 marked on it, and having two fine platinum wires melted into its upper 

 end, with their free-ends projecting into the tube (p and ??-). 



(1.) Estimation Of the COs. A small ball of fused caustic potash, fixed on a 

 platinum wire, is introduced into the mixture of gases through the lower end of 

 the eudiometer under cover of the mercury. The surface of the potash ball it 

 moistened before it is introduced. The C0 2 unites with the potash to form 

 potassium carbonate. After it has been in for a considerable time (24 hours), it 

 is withdrawn iu a similar manner. The diminution in volume indicates the 

 amount of C0 2 absorbed. 



(2.) Estimation Of the 0. () Just as in estimating the COo. a ball of phos- 

 phorus on a platinum wire is introduced into the eudiometer (Bertholet); it 

 absorbs the and forms phosphoric acid. Another plan is to employ a small 

 papier-mache ball saturated with pyrogalliQ acid in caustic potash, which rapidly 

 absorbs (Liebig). After the ball is removed, the diminution in volume 

 indicates the quantity of 0. 



(b.) The is most easily and accurately estimated by exploding it in the 

 eudiometer (Volta and Bunsen). Introduce a sufficient quantity of H into 

 the eudiometer, and accurately ascertain its volume ; an electrical spark is 

 now passed between the wires, p and n, through the mixture of gases ; the and H 

 unite to form water, which causes a diminution in the volume of the gases in the 

 eudiometer, of which ^ is due to the used to form water (H 2 0). 



(c.) Estimation Of the N. When the C0 2 and are estimated by the above 

 method, the remainder is pure N. 



36. The Blood Gases. 



I. Oxygen exists in arterial blood (dog) on an average to the 

 extent of 17 volumes per cent, (at 0C. and 1 metre Hg pressure) 

 (Pfliiger). According to Pfliiger, arterial blood (dog) is saturated to 

 ^ with 0, while, according to Hu'fner, it is saturated to the extent 

 of yi. In venous blood the quantity varies very greatly; in the blood 

 of a passive muscle 6 volumes per cent, have been found ; while in the 

 blood after asphyxia it is absent, or occurs only in traces. It is 

 certainly more abundant in the comparatively red blood of active 

 glands (salivary glands, kidney), than in ordinary dark venous blood. 



The in Blood occurs (a.) simply absorbed in the plasma. This is 

 only a minimal amount, and does not exceed what distilled water 

 at the temperature of the body would take up at the partial pressure 

 of the in the air of the lungs (Lothar Meyer). According to 



