GASES IN THE BLOOD. 357 



Another conclusive proof that the union of the O with the 

 haemoglobin is really a chemical one, is given by the spectroscopic 

 examination of a hsemoglobin solution. When deprived of its 

 O, and after the admixture of the air, quite dissimilar spectra 

 are seen, as already pointed out in Chapter XIV. (Fig. 107.) 



The amount of O taken up by the blood is not always in pro- 

 portion to the pressure of that gas, but rather to the amount of 

 hsemoglobin in the blood ; and we therefore find the adequacy of 

 the respiratory function of the blood going hand in hand with 

 its richness in hsemoglobin, and thus the "shortness of breath" 

 of ansemic and chlorotic individuals is explained. 



Our knowledge concerning the relation of the CO 2 to the con- 

 stituents of the blood is less definite and clear. 



It does not altogether exist as a mere physical solution, for it 

 comes off irregularly under the air pump, and does not obey 

 exactly the Henry-Dalton law of the absorption of gases. Part 

 comes off easily and part with difficulty. It is not associated 

 with the corpuscles, for more of this gas can be obtained from 

 serum than from a like quantity of blood. It is more easily re- 

 moved from the blood than from the serum, a certain proportion 

 (about 7 per cent, of the whole) remaining, in the serum in vacuo, 

 until dissociated by the addition of an acid or a piece of clot 

 containing corpuscles. If bicarbonate of soda be added to blood 

 from which all the gas has been removed, still more CO 2 can be 

 pumped out, from which it would appear that something exists in 

 the blood capable of dissociating CO* from sodium bicarbonate. 



It has been suggested that the CO 2 is in some way associated 

 (possibly as sodium bicarbonate) with the plasma of the blood, 

 and that the corpuscles have the power of acting like a weak 

 acid, and of dissociating it from the soda, and thus raising its 

 tension in the blood. 



The great importance of the chemical nature of the union 

 between the O and hsemoglobin for external respiration becomes 

 most striking when the actual manner in which the entrance of 

 the O is effected is taken into account. 



It must be remembered that the further we trace the air down 

 the passages, the less will be the percentage of O found in it, and 



