1116 



PHYSIOLOGY 



70 



The carbon dioxide is contained chiefly in theplasma, though a certain 

 amount is also in combination in the corpuscles. Part of the carbon dioxide 

 must be in combination with some constituent common to both plasma 

 and corpuscles. When blood plasma is calcined, the ash is found to be 

 distinctly alkaline and to contain an amount of sodium greater than is 



necessary to combine with 

 . the other acid radicals, e. g. 

 01, S0 4 , and P0 4 , and this 

 excess becomes greater if we 

 consider that a large part of 

 the P0 4 and S0 4 is derived 

 from the oxidation of the 

 sulphur and phosphorus pre- 

 sent in organic combination 

 in the plasma. We may 

 therefore conclude that a con- 

 siderable part of the carbon 

 dioxide exists in the plasma 

 as sodium bicarbonate. 



The question arises 

 whether the whole of the 

 combined carbonic acid of 

 the blood can be regarded 

 as existing in the form of 

 sodium bicarbonate. Ac- 

 cording to the analyses of 



This curve shows the influence of the saturation of Carl Schmidt given on page 



the haemoglobin with oxygen on the amount of C0 a 



taken up by the blood at various pressures. 

 Upper curve = absorption of C0 2 by human blood in 



50 



40 



Fio. 612. Curve of C0 2 tension in blood. 

 ( CHRISTIANSEN, DOUGLAS and HALDANE.) 



909, the blood contains 

 4-31 x 1(T 2 N sodium. On 



presence of hydrogen and C0 8 . . , , , . , 



Middle curve = absorption of C0 2 by human blood in saturating blood With car- 



presence of air and CO 8 . bonic acid and makin 



Lower curve = absorption of C0 2 in blood of ox and 



dog in presence of air. 

 The thick line A-B represents the absorption of C0 a by 



human blood within the body (supposing the blood 



is completely deoxygenated in the tissues). 

 ide 



bonic acid and making 



. 



allowance for the amount 



n f fhj Q ^OQ i n aim-nip Q^IT, 



tion, it is found that 100 CC. 

 o f }a nnr j ^11 f fl T, p 11T > a h nil f 



100 C.C. of Carbonic acid ill 



It is evident that an increase of 15 c.c. per cent, of C0 2 

 in the blood, as it passes through the tissues, would 

 raise the tension of this gas in the blood only 



22 mm. Hg. (from 40 to 62). Under normal con- rt i rt1 nn -\ ^t,- -: A 

 ditions the rise of CO 2 pressure in the blood on Chemical combination. As- 

 passing through the tissues is not more than 5-7 suming this to exist entirely 





in combination with sodium, 



it would correspond to a concentration of about 4-5 X 10~ 2 N sodium. 

 This would be equivalent to 0-1035 per cent, sodium, or to 0'378 

 per cent, sodium bicarbonate in the whole blood. A difficulty in 

 assuming that all the carbonic acid is in the form of sodium bicarbonate is 

 presented by the fact that the behaviour of blood, when exposed to varying 

 pressures of carbon dioxide, differs markedly from that of a solution of 

 sodium bicarbonate. In Fig. 513 this difference is represented graphically. 



