DEVELOPMENT OF THE RED BLOOD-CORPUSCLES 



111 



globin then makes its appearance in certain of these nucleated embryonal 

 cells, which thus become the earliest red blood-corpuscles. The proto- 

 plasm of the cells and their branched network in which these corpuscles 

 lie then become hollowed out into a system of canals enclosing fluid, in which 

 the red nucleated corpuscles float. The corpuscles at first are from about 

 10 /A to 16 p, in diameter, mostly spherical, and with granular contents, and 

 a well-marked nucleus. Their nuclei, which are about 5 p in diameter, 



FIG. i 



PIG. 114. 



FIG. 113. Multiplication of the Nucleated Red Corpuscles. Marrow of young kitten after 

 bleeding, showing above karyo kinetic division of erythroblast, and below the formation of mature 

 from immature erythrocytes. (Howell.) 



FIG. 114. Shows the Way in which the Nucleus Escapes from the Nucleated Red Corpuscles. 

 1,2,3, 4, represent different stages of the extrusion noticed upon the living corpuscles, a, Specimen 

 from the circulating blood of an adult cat, bled four times; b, specimen from the circulating blood 

 of a kitten forty days old, bled twice; c, specimens from the blood of a fetal cat, 9 cm. long. Others 

 from the marrow of an adult cat, two of the figures showing the granules present in the corpuscles, 

 which have been interpreted erroneously as a sign of the disintegration of the nucleus. (Howell.) 



are central, circular, very little prominent on the surfaces of the corpuscles, 

 and apparently slightly granular. 



The corpuscles then strongly resemble the colorless corpuscles of the 

 fully developed blood but for their color. They are capable of ameboid 

 movement and multiply by division. 



When, in the progress of embryonic development, the liver is formed, 

 the multiplication of blood-cells in the whole mass of blood ceases, and new 

 blood-cells are produced by this organ, and also by the spleen. These are 

 at first colorless and nucleated, but afterward acquire the ordinary blood tinge, 

 and resemble very much those of the first set. They also multiply by division. 

 The bone marrow also begins to form red corpuscles, though at first in small 

 amounts only. This function develops rapidly, however, so that at birth 

 the marrow represents the chief seat of production of the red cells. Never- 

 theless, nucleated red cells are usually found at birth, sometimes in con- 

 siderable quantities in the liver and in the spleen. Non-nucleated red cells 

 begin to appear soon after the first month of fetal life, and gradually increase 

 so that at the fourth month they form one-fourth of the whole amount of 



