42 ESTIMATION OF THE BLOOD GASES. 



analyses it is difficult to do this, and the best plan to pursue in that case is to keep the recep- 

 tacles containing the blood on ice. 



Mayow (1670) observed that gases were given off from blood in vacuo. Magnus (1837) in- 

 vestigated the percentage composition of the blood gases. The more important recent investi- 

 gations have been made by Lothar Meyer (1857), and by the pupils of C. Ludwig and E. 

 Pfliiger. . 



35. QUANTITATIVE ESTIMATION OF THE BLOOD GASES. The gases 

 obtained from blood consist of O, C0 2 , and N. Pfliiger obtained (at C. and 1 

 metre Hg pressure) 47*3 volumes per cent., consisting of 



0, 169 per cent. ; C0 2 , 29 per cent.; N, 1*4 per cent. 

 As is shown in fig. 22, J, the gases are obtained in an eudiometer, i.e., in a narrow 

 tube, 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 n). 



(1) Estimation of the CO.,. 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 is moistened before it is introduced. The CO s 

 unites with the potash to form potassium carbonate. The potash bulb is withdrawn after 24 

 hours. The diminution in volume indicates the amount of C0. 2 absorbed. 



(2) Estimation of the 0.{a) Just as in estimating the C0 2 , a ball of phosphorus on a 

 platinum wire is introduced into the eudiometer ; it absorbs the and forms phosphoric acid. 

 Another plan is to employ a small papier-mache ball saturated with pyrogallic acid in caustic 

 potash, which rapidly absorbs 0. After the ball is removed, the diminution in volume indicates 

 the quantity of 0. 



(h) The is most easily and accurately estimated by exploding it in the eudiometer. Intro- 

 duce 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 eudio- 

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



(r) Estimation of the N. When the C0 2 and are estimated by the above method, the 

 remainder is pure N. 



36. THE BLOOD GASES. [In human blood the average total gases are 

 estimated to be, at C. and 1 metre pressure, 



CO, N 



Arterial blood, 17 30 1 to 2 per cent. 



Venous blood, 6 to 10 35 1 to 2 

 or, calculated at C. and 760 mm. pressure, 



Arterial blood, 20 39 1*4 per cent. 



Venous blood, 8 to 12 46 1*4 ] 



I. Oxygen exists in arterial blood (dog) on an average to the extent of 17 

 volumes per cent, (at C. and 1 metre Hg pressure) (PJlwjer). According to 

 pfliiger, arterial blood (dog) is saturated to T \ with O, while, according to Hiifner, 

 it is saturated to the extent of if 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. 



[Modifying Conditions. The amount of obtainable from the blood depends upon the organ 

 inthe C meS ' r whether the or an be active or at rest - Thlls the present 



Carotid artery is . . 21 per cent. I Renal vein (kidney active), 17 per cent. 



Renal artery, . . 19 | Renal vein (kidney at rest), 6 



Bert finds that increase of the atmospheric pressure from 1 to 10 atmospheres raises the 



^TZl ?-!\ a rn - b w -T, 20 I 0V f\ 24 I* 1 ' cent " and the N from 1-8 to over 9 

 per cent., while the CO s is but slightly affected.] 



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



