258 OF THE BLOOD: 



of the plasma. A small proportion of Nitrogen and traces of Ammonia are, 

 however, constantly present. In 100 volumes of blood are found between 50 

 and 60 volumes of these gases collectively (namely, in arterial blood C0 2 

 30-35 vol., O 16-20 vol., and N 1 or 2 vol., in venous CO, 40-50 vol., O 12 vol., 

 N 1 or 2 vol.); but their total quantity, as well as their relative proportions, 

 present considerable variations in different parts of the body. From the 

 results of numerous recent researches the conclusions may be drawn, that 

 the affinity or capacity of absorption of the blood for the two first-named 

 gases at least, is peculiar, follows laws of its own, and differs materially 

 from that of other liquids. If we compare it, for instance, with water, we 

 find that whilst 100 vol. of water will take up 2.97 vol. of Oxygen at stand- 

 ard temperature and pressure, the same quantity of blood, at 32 F., will 

 absorb from 16.882 vol. to 19.794 vol.; 1 and the amount absorbed appears 

 to be but slightly affected by the degree of pressure to which the fluid is 

 subjected (Bert), though according to the experiments of Bernard 2 it varies 

 to a considerable extent in blood drawn from different regions of the body. 

 Thus whilst 100 vol. of arterial blood which already contained a consider- 

 able amount absorbed only 8.9 vol. of Oxygen, the same quantity of blood 

 taken from the Jugular Vein absorbed 16 vol., from the Right Heart 21.1 

 vol., and from the Portal Vein 30 vol. of this gas, and Grehant found that 

 the arterial blood of a dog contained 16.3 vol. per cent, of Oxygen, but if 

 the animal were made to breathe O, the proportion rose to 23.3 per cent., 

 whilst if it were agitated with oxygen out of the body it contained 26.8 per 

 cent. In ordinary air the tension of the oxygen is equal to a column of 

 mercury 158 mm. in height, corresponding to 20.8 per cent, by volume; but 

 the tension of the oxygen in the blood is, in consequence of its affinity for 

 hemoglobin, very low, amounting in the case of the arterial blood of the 

 dog to a mean of only 22 mm. of mercury, 3 that is to say, it corresponds to 

 the tension of oxygen in an atmosphere containing 2.9 per cent of this gas; 

 in the venous blood it amounts to 29.6 mm. (3.9 per cent.). For complete 

 saturation the pressure of the oxygen in the atmosphere or in the blood 

 must amount to between 20 and 30 mm. With increase of temperature the 

 affinity of haemoglobin for oxygen diminishes, whilst with diminished tem- 

 perature it increases, or in other words the quantity of oxygen absorbed by 

 the blood varies inversely with the temperature of the air inspired. 4 In a 

 similar manner, whilst 100 vol. of water will absorb about 100 vol. of Car- 

 bonic acid at ordinary temperature and pressure, Meyer 5 found that 100 

 vol. of fresh defibrinated blood would take up 178.3 vol. of Carbonic acid at 

 48 F., the quantity increasing, though not in direct proportion, with the 

 pressure. The tension of the CO 2 in ordinary air amounts to 0.38 mm., cor- 

 responding to 0.05 per cent, by volume; but in arterial blood it amounts on 

 its average to 21 mm., i.e., to the tension of the gas in an atmosphere con- 

 taining 2.8 per cent.; and in venous blood to 41 mm., or to the tension of 

 the gas in an atmosphere containing 5.4 per cent. 6 Even as regards Nitro- 



1 Setschenow, Beitriigc zur Pneumatologie des Blutes, Sitzungsbcricht d. k. Akad. 

 d. Wissens., xxxvi, 1859, p. 293. See also Fernet, Annul, do Scien. Nat., 1858, turn, 

 viii, ]). 125. Grehant, Corn pies Rendus, Ixxv, p. 495. 



2 Lo9ons, is.')!), torn, i, p. 282. 



3 See Worm Miiller, Bericht d. Sachs. Gesellschaft, 1870, p. 351. See also Her- 

 mann, Physiologic, 1S74, p. 140. 



4 .Matlii(!ti and D'Urbain, Archives de Physiologie, No. 5, 1872. See also Estor 

 and St. Pierre, Journal de I'Anatomie, 1805. 



5 Zcil-ehrift f. Rat. Mod., Bd. viii, p. 256. 



6 See Hermann, op cit., p. 140, quoted from Strassburg. Wolffberg, Pfl Tiger's 

 Arehiv, Bd. iv, Ilet't x, found the tension of the O in the blood of the, pulmonary 

 capillaries amounted to 27 mm. of mercury, and that of the CO 2 to 24 mm. 



