y40 PHYSIOLOGY 



adult life. In an adult the total volume of blood and the total number 

 of corpuscles remain approximately constant. By bleeding an animal 

 we can diminish the total amount of corpuscles. The first effect of 

 such a bleeding is that the fluid parts of the blood are made up, so 

 that the volume of the blood is restored to normal and the blood 

 therefore becomes relatively poor in corpuscles. In a few weeks, 



FIG. 360. Part of a blood-vessel from the yolk-sac of the rabbit embryo, 

 showing the changes which occur in the formation of erythrocytes. 

 (From SCHAFER after MAXIMOW ) 

 a, megaloblasts ; &, normoblasts changing into erythroblasts ; c, ery- 



throblasts, in which the nuclei are disappearing ; d, an erythrocyte 



fully formed, but not yet disc-shaped ; en, phagocytic endothelial cells ; 



I, lymphocytes ; k, a divided lymphocyte ; n, erythroblasts, shrunken 



with atrophic nucleus. 



however, the corpuscular content of the blood is found to be once 

 more normal, showing that the loss of corpuscles has been followed by 

 a compensatory regeneration. The fact that the pigments constantly 

 leaving the body with the urine and faeces, namely, urochrome and 

 urobiiin or stercobilin, are derived by means of the liver from haemo- 

 globin, shows that a constant destruction of red corpuscles must be 

 proceeding. Since the number of corpuscles remains unaltered, this 

 loss of haemoglobin must be made good by a continual regeneration of 



