730 SPECIAL PHYSIOLOGY. 



noplast; but a distinct, though delicate, envelope or cell-wall afterwards 

 appears. The difference between them appears to be, that in the Mammalian 

 red corpuscle the envelope touches the nucleus, around which there are no cell- 

 contents, or the nucleus disappears in these; whilst in the other Yertebrata, 

 the envelope is at a distance from the nucleus, the cell-contents being abun- 

 dant. The importance of the nucleus, as a centre of activity, is thus well 

 illustrated. 



The chemical changes in the corpuscles are no less remarkable than 

 those which affect their form. Their globulin acquires phosphorus and 

 iron, the former element associated with fat, and the latter with the 

 coloring matter or cruorin. They now also manifest a singular 

 affinity for oxygen. It is not quite certain in what part of the circu- 

 lation the change of white into red corpuscles takes place ; but it is 

 supposed that this is completed during the passage of the venous blood, 

 in which the white corpuscles abound, through the capillaries of the 

 lungs; they are fewer in the arterial blood. The remarkable eifects of 

 the respiratory process on the blood, and the strong affinity of the red 

 corpuscles themselves, when fully formed, for oxygen, prove that the 

 oxygenation of the blood, which takes place in the lungs, is accom- 

 panied by changes of deep importance in its corpuscles, and favor the 

 idea that it may even be concerned in the conversion of the white cor- 

 puscles into red ones. 



It has been already stated that the red corpuscles, after enduring 

 or living a certain time, waste or die. Many writers have supposed 

 that they accumulate in the spleen, becoming impacted, as it were, in 

 the venous sinuses of that organ, and then shrinking and disappearing. 

 By others, again, it is believed that the cruorin, or red coloring mat- 

 ter, is added to the young corpuscles in this organ, perhaps even from 

 the debris of these red corpuscles, which become stagnated and disin- 

 tegrated in it. 



Besides the corpuscles, however, the intercellular fluid matrix of 

 the blood, or liquor sanguinis, is, as we have seen, constantly under- 

 going loss, in supplying the materials necessary for the maintenance 

 and formation of the great variety of tissues and secretions. Every 

 act of nutrition, like those of secretion, must remove something from, 

 and so far impoverish, the blood. The albumen of the liquor san- 

 guinis is constantly replenished from that of the lymph and chyle, and, 

 by venous absorption, from the digested food ; but it may also con- 

 tain certain more highly elaborated albuminoid materials, derived from 

 the corpuscles. Some of the substances employed in nutrition, such as 

 the salts and earthy matters, may belong properly to, and proceed 

 from, the liquor sanguinis itself; so also may certain albuminoid mat- 

 ters. But others may merely traverse that fluid, on their way from 

 the blood corpuscles, in which they are finally completed, to the tissues, 

 escaping through the envelopes of the corpuscles, by dialysis or exos- 

 mosis, passing across the liquor sanguinis, by liquid diffusion, and then 

 permeating the capillary walls, by dialytic or porous diffusion ; so like- 

 wise of the fatty matters, which must be immediately added to the 

 blood from the nutrient chyle. Some substances, of a more special 

 kind, may be formed by changes in the corpuscles, and may after- 



