92 



HANDBOOK OF PHYSIOLOGY. 



ular meshwork. The nuclei increase in number, and collect chiefly in 

 the larger masses of protoplasm, but partly also in the processes. These 

 nuclei gather around them a certain amount of the protoplasm, and be- 

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

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

 come hollowed out into a system of canals inclosing fluid, in which the 

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

 mhro to TtW ^ an i ncn i n diameter, mostly spherical, and with granular 

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

 WOT ^ an i ncn i n diameter, are central, circular, very little prominent 

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

 tuberculated. 



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 arid 

 nucleated, but afterwards 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 fcetal life to be 

 mingled with colored non-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 Colored Corpuscles. The non-nucleated 

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

 probability are an entirely new formation, and the methods of their ori- 



FIG. 84. Development of red corpuscles in connective-tissue cells. From the subcutaneous 

 tissue of a new-born rat. h, a cell containing haemoglobin in a diffused form in the protoplasm ; h', 

 one containing colored globules of varying size and vacuoles ; h", a cell filled with colored globules 

 of nearly uniform size ; /, /', developing fat cells. (E. A. Schafer.) 



gin are the following : (1.) During foetal life and possibly in some ani- 

 mals, 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 



