524 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



quantity of gas combined with the haemoglobin would be equal to 23.38 vol- 

 umes per cent, of the blood; in other words, arterial blood should contain 

 23.38 volumes per cent, of O. This, however, is more than is found, but the 

 deficit is accounted for by the fact that only from -fo (Pfluger) to ^ (Hiifner) 

 of the hemoglobin is saturated. 



The plasma and the serum absorb but very small quantities of O according 

 to Pfluger, only 0.26 volume per cent. Owing to the relatively low absorption- 

 coefficient of the plasma compared with the O-capacity of the haemoglobin, as 

 well as to the fact that the hemoglobin is practically saturated at a relatively low 

 pressure, the quantity of O absorbed is not materially affected by an increase of 

 pressure above the level of the tension of dissociation the slight increase which 

 does occur is due chiefly to absorption by the plasma. 



The tension of O in arterial and venous blood must be ascertained separately, 

 inasmuch as each contains a different percentage. Following this method, 

 Strassburg 1 records the following averages: Arterial blood, 29.64 millimeters 

 of Hg, or 3.9 per cent, of an atmosphere ; and venous blood, 22.04 millimeters, 

 or 2.9 per cent, of an atmosphere. 



Tension of C0 2 . Venous blood contains about 45 volumes per cent, of 

 CO 2 . The results of experiments prove that only about 5 per cent, of this 

 CO 2 is in simple solution, that from 10 to 20 per cent, is in firm chemical 

 combination, and that from 75 to 85 per cent, is in loose combination. 



When the blood at the temperature of the body is subjected to a vacuum, 

 all of the CO 2 is given off; but if the blood-corpuscles be removed and the 

 plasma and corpuscles each in turn be submitted to the pump, both will give 

 off CO 2 , the plasma yielding a larger volume than the corpuscles, but not so 

 much as when they are together. Plasma and serum in vacuo give off only a 

 portion of their CO 2 ; the remainder may, however, be dissociated by adding 

 acid or red corpuscles. The red corpuscles therefore act as an acid and cause the 

 disengagement of all the gas from the plasma ; consequently, not only do the 

 corpuscles yield up the CO 2 contained in them, but they are also active agents 

 in bringing about the dissociation of CO 2 which is in chemical combination in 

 the plasma. The dissociation is due in part, perhaps, to the presence of phos- 

 phates in the stromata of the red corpuscles, and to certain proteids, but the 

 observations of Preyer and Hoppe-Seyler lead to the conviction that it is due 

 chiefly to oxyhemoglobin and haemoglobin. Phosphates, proteids, haemoglobin, 

 and oxyhsemoglobin all have the power of expelling CO 2 from sodium car- 

 bonate in solution in vacuo, but this fact leaves us none the wiser as to which, 

 if any, is active in this way in the blood. Arterial blood gives off its CO 2 

 more readily than venous blood. 



Of the total quantity of CO 2 , about 5 per cent, is in simple solution and 

 from 10 to 20 per cent, is in firm chemical combination in the plasma, the latter 

 requiring the addition of acid or of haemoglobin, etc. to cause its dissociation 

 in vacuo ; while the remainder, constituting much the larger proportion, is in 

 loose chemical union in both the plasma and the corpuscles. That which is in 



1 Pflilger's Archiv fur Physiologic, vol. vi. p. 65. 



