304 THE BLOOD. [CHAP. XXVII. 



Function of the Red Corpuscles. It is clear that the red cor- 

 puscles must perform some very important office in the life of the 

 blood, because of their great numbers, their constancy, and the 

 serious consequences to the general nutrition and the vital actions 

 of the body, which ensue upon any considerable diminution in the 

 quantity of them. But we have no definite knowledge on this sub- 

 ject ; and all that can be suggested is, as yet, of a speculative and 

 hypothetical nature. 



Liebig adopted the highly ingenious notion that the red cor- 

 puscles are carriers of oxygen, and that by their colouring matter 

 they are peculiarly adapted for attracting that principle. The 

 property of attracting oxygen is due to the iron, which forms six 

 per cent, of the haematine contained in the red corpuscle. In 

 venous blood, according to Liebig, the iron is in the state of 

 carbonate of the protoxide of iron ; this, as the blood passes 

 through the capillaries of the lungs, or becomes otherwise exposed 

 to the action of the air, is by the absorption of oxygen converted 

 into the hydrated peroxide of iron, the state in which that metal 

 exists in arterial blood. And at the same time it gives off " for 

 every volume of oxygen necessary for the change from protoxide to 

 peroxide, four volumes of carbonic acid." As the arterial blood 

 passes through the capillaries of the system, the peroxide of iron 

 yields oxygen to certain constituents of the body, which is em- 

 ployed in producing the change of matter, and in oxidising newly- 

 formed substances in the blood, while, in their return towards the 

 heart, the red particles which had lost their oxygen "combine 

 with carbonic acid, producing venous blood ; and when they reach 

 the lungs an exchange takes place between this carbonic acid and 

 the oxygen of the atmosphere." 



This doctrine of Liebig assigns the use of the colouring matter, 

 or of the contents of the blood-corpuscle, rather than of the 

 corpuscle itself; it is, indeed, highly reasonable to suppose that 

 the haematine has an important connection with the attraction 

 of oxygen into the system, or to speak more generally, with the 

 changes which take place in the blood in respiration. The differ- 

 ence of colour, being the prominent feature of distinction between 

 arterial and venous blood is strongly indicative of this ; and also 

 the fact now demonstrated by Mr. Wharton Jones, that the 

 blood of the invertebrata contains a certain degree of colour, or at 

 any rate, even where no colour can be distinguished, according to 

 Professor Graham's analysis, " a sensible quantity of iron, perhaps, 

 as much as red corpuscles." 



