62 THE HUMAN BODY. 



Higher and more complex animals need more oxygen and, as 

 blood-plasma dissolves very little of that gas, they develop in 

 addition the haemoglobin-containing corpuscles which pick 

 it up in the gills or lungs and carry it to all parts of the 

 Body, leaving it where wanted (see Chap. XXVI). In cold- 

 blooded vertebrates the red corpuscles are not nearly so many 

 in proportion as in the warm-blooded, which use far more 

 oxygen. The older view, was that the mammalian red cor- 

 puscle represented the nucleus of one of the white, in which 

 haemoglobin had been formed and from about which the rest 

 of the corpuscle had disappeared. This, however, does not 

 seem to be the case. In adults new red blood -corpuscles are 

 formed by the segregation of portions of the protoplasm of 

 peculiar cells (hcematoblasts) found in various parts of the 

 Body, but especially in the red marrow of certain bones (p. 

 95). In the embryo some cells of the liver, and in new-born 

 animals (possibly also in adult) some connective-tissue cor- 

 puscles (p. 112) form new red blood-corpuscles. 



How long an individual red corpuscle lasts is not known, 

 nor with certainty how or where it disappears : there is, how- 

 ever, some reason to believe that many are finally destroyed 

 in the spleen (see Chap. XXIII). Their average rate of dis- 

 appearance and new formation is unknown, but in emergen- 

 cies (as after severe haemorrhages) they can be reproduced 

 with great rapidity. 



Chemistry of Lymph. Lymph is a colorless fluid when 

 pure, feebly alkaline, and with a specific gravity of about 

 1045. It may be described as blood minus its red corpuscles 

 and much diluted, but of course in various parts of the Body 

 it will contain minute quantities of substances derived from 

 neighboring tissues. It contains a considerable quantity of 

 carbon dioxide gas which it gives up in a vacuum, but no un- 

 combined oxygen, since any of that gas which passes into it 

 by diffusion from the blood is immediately picked up by the 

 living tissues among which the lymph flows. 



