USES OF THE BLOOD. 87 



The phosphate and carbonate of sodium, besides maintaining 

 the alkalinity of the blood, are said especially to preserve the 

 liquidity of its albumen, and to favor its circulation through 

 the capillaries, at the same time that they increase the absorp- 

 tive power of the serum for gases. But although, from the 

 constant presence of a certain quantity of saline matter in the 

 blood, we may believe that it has these last-mentioned impor- 

 tant functions in connection with the blood itself, apart from 

 the nutrition of the body, yet, from the amount which is daily 

 separated by the different excretory organs, and especially by 

 the kidneys, w r e must also believe that a considerable quantity 

 simply passes through the blood, both from the food and from 

 the tissues, as a temporary and useless constituent, to be ex- 

 creted when opportunity offers. 



Corpuscles. The uses of the red corpuscles are probably not 

 yet fully known, but they may be inferred, at least in part, 

 from the composition and properties of their contents. The 

 affinity of haemoglobin for oxygen has been already mentioned ; 

 and the main function of the red corpuscles seems to be the 

 absorption of oxygen in the lungs by means of this constitu- 

 ent, and its conveyance to all parts of the body, especially to 

 those tissues, the nervous and muscular, the discharge of whose 

 functions depends in so great a degree upon a rapid and full 

 supply of this element. The readiness with which haemoglo- 

 bin absorbs oxygen, and delivers it up again to a reducing 

 agent, so well shown by the experiments of Prof. Stokes, ad- 

 mirably adapts it for this purpose. How far the red corpus- 

 cles are concerned in the nutrition of the tissues is quite un- 

 known. 



The relation of the white to the red corpuscles of the blood 

 has been already considered (p. 83); of the functions of the 

 former, other than are concerned in this relationship, nothing 

 is positively known. Recent observations of the migration of 

 the white corpuscles from the interior of the bloodvessels into 

 the surrounding tissues (see section, On the Circulation in the 

 Capillaries) have, however, opened out a large field for inves- 

 tigation of their probable functions in connection with the nu- 

 trition of the textures, in which, even in health, they appear 

 to wander. 



