416 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



that 100 cubic centimeters of blood contain 1 5 grams of haemoglobin (p. 

 37), the quantity of gas which would combine with this amount of haemo- 

 globin would be equal to 20.1 cubic centimeters ; in other words, arterial 

 blood should contain, if the haemoglobin be saturated with oxygen, 20.1 

 volumes per cent, of ( >. 



The plasma ami the serum absorb hut very small quantities of O — accord- 

 ing to PHiiger, only 0.26 volume per cent. ( hving to the relatively low absorp- 

 tion-coefficient of the plasma compared with the ( ^capacity of the haemoglobin, 

 as well as to the fact that the haemoglobin is nearly 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 tension of O in arterial and venous blood must be ascertained separ- 

 ately, 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. The figures obtained 

 by Bohr and by Ilaldane and Smith 2 are, however, much higher (see p. 418). 



Tension of ( '0 2 . — Venous blood contains about 45 volumes per cent, of 

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

 ( '( )., 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 C0 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,, 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 C0 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 C0 2 contained in them, but they are also active agents 

 in bringing about the dissociation of CO z 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. While phosphates, proteids, 

 haemoglobin, and oxyhemoglobin all may have the power of expelling C0 2 

 from sodium carbonate in solution in vacuo, this fact leaves us none the wiser 

 as to which, if any, is active in this way in the blood. Arterial blood gives 

 oil' its CO., more readily than venous blood. 



Of the total quantity of 0O 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 



1 Archivfiir Physiologic, Bd. vi. S. 65. 



2 Journal of Physiology, 1<S!*7, vol. xxii. p. 231. 



