CHAP, xvi.] PHYSIOLOGICAL OFFICE OF RESPIRATION. 247 



themselves with it, and convey it to the capillary vessels of fine 

 calibre, which penetrate the very web of the tissues. But tnis 

 part of the system of circulation is the special Jfold of nutritive 

 exchanges. There, in effect, the blood is no longer separated 

 from the anatomical elements and the liquids which bathe them, 

 except by the thin homogeneous partition of the capillaries. 

 The blood then yields to the tissues assimilable materials and 

 takes back disassimilated materials. In the first category is 

 comprehended oxygen ; in the second, carbonic acid. Without 

 the incessant access of the first, without the incessant expulsion 

 of the second, the succession of chemical reactions and transfor- 

 mations, which, as a whole constitute nutrition, would cease to 

 take place ; the whole vital movement would be retarded and 

 stopped. 



The oxygen is not simply dissolved in the substance of the 

 sanguineous globule ; it seems to be combined with this substance. 

 In effect, if we inject into the veins of a dog an eager absorbent 

 of oxygen, for example, pyro-gallic acid, the animal does not ap- 

 pear sensible of it ; its globules do not part with their provision 

 of oxygen. 1 On the contrary, certain substances, which are 

 capable of yielding oxygen, are deprived of it in the blood ; the 

 globules carry it away from them. Thus, per-oxyde of iron 

 injected into the circulation, is found again in the urine as pro- 

 toxyde. The globules may be considered as condensers of 

 oxygen ; they are pre-eminently the exciting agents of life ; also, in 

 the operation of transfusion it is sufficient to inject into the veins 

 defibrinated blood; probably the globules alone would suffice. 

 Certain substances have the property of killing the globules, 

 of rendering them for ever unfit for the absorption of 

 oxygen. Such is particularly oxyde of carbon ; but even in cases 

 of poisoning, by this substance, persons have often succeeded in 

 reviving the poisoned animals, in resuscitating them by having 

 recourse to transfusion, that is to say, by replacing the dead 

 globules with living ones. 



1 Cl. Bernard, Lemons sur lesLiquides de VOrganisme. 



