THE BLOOD. 



97 



coming colored, form the red blood corpuscles. The protoplasm of the 

 cells and their branched network in which these corpuscles lie then be- 

 comes hollowed out into a system of canals enclosing fluid, in which the 

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

 g-sW ^0 TsW t an i ncn i* 1 diameter, mostly spherical, and with granular 

 contents, and a well-marked nucleus. Their nuclei, which are about 

 5^0- of an inch in diameter, are central, circular, very little prominent 

 on the surfaces of the corpuscle, and apparently slightly granular or tu- 

 berculated. 



The corpuscles then strongly resemble the colorless corpuscles of the 

 fully developed blood, but are colored. They are capable of amoeboid 

 movement and multiply by division. 



When, in the progress of embryonic development, the liver begins to 

 be 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 

 lymphatic glands, thymus and 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. In 

 whichever way produced, however, whether from the original formative 

 cells of the embryo, or by the liver and the other organs mentioned 

 above, these colored nucleated cells begin very early in foetal life to be 

 mingled with colored wcw-nucleated corpuscles resembling those of the 

 adult, and at about the fourth or fifth month of embryonic existence are 

 completely replaced by them. 



Origin of the Mature Red Corpuscles. The non-nucleated red 

 corpuscles may possibly be derived from the nucleated, but in all proba- 

 bility are an entirely new formation, and the methods of their origin are 



uniform size; /, /', developing fat cells. (E. A. SchSfer.) 



the following: (1.) During foetal life and possibly in some animals, e.g., 

 the rat, which are born in an immature condition, for some little time after 

 birth, the blood discs arise in the connective tissue cells in the following 

 way. Small globules, of varying size, of coloring matter arise in the 

 protoplasm of the cells, and the cells themselves become branched, their 

 branches joining the branches of similar cells. The cells next become 

 VOL. I. 7. 



