THE RED BLOOD CORPUSCLES 



875 



attainment of full stature by the animal. \\% have definite proof that a 

 continual formation of red corpuscles can proceed and is proceeding 

 throughout the whole of 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 



FIG. 375. Part of a blood vessel from the yolk sac of the rabbit embryo, showing 

 the changes which occur in the formation of erythrocytes. (From SCHAFEB 

 after MAXIMO w.) 



a, megaloblasts ; 6, normoblasts changing into erythro blasts ; c, erythroblasts, 

 in which the nuclei are disappearing ; d, an ery throcy te fully formed, but not yet disc 

 shaped; en, phagocytic endothelial cells.; /, lymphocytes; k, a divided lymphocyte; 

 n, erythroblasts, shrunken with atrophic nucleus. 



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

 are derived by means of the liver from haemoglobin, 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 fresh haemoglobin and new red corpuscles. 

 The seat of the formation of red corpuscles in the higher vertebrates is the 



