No. I.] BLOOD CORPUSCLES. 



113 



acter of the nucleus and the amount of haemoglobin. This 

 latter form multiplies by karyokinesis, and the daughter-cells 

 sooner or later appear as mature nucleated red corpuscles, 

 which then lose their nuclei by extrusion, and become non- 

 nucleated red corpuscles. The biconcavity of the red corpus- 

 cles is probably caused in the first place by the removal of the 

 nucleus from the middle of the spherical cell. The liberated 

 nuclei go into solution in the blood plasma, and probably form 

 or help to form the fibrinogen of the plasma. The immature 

 or young nucleated red corpuscles are derived from spherical 

 colorless cells, erythroblasts, having a definite histological struc- 

 ture and found in the marrow. These cells multiply actively 

 by karyokinesis. The erythroblasts in turn are derived from 

 larger embryonic cells, usually described in the adult as ordi- 

 nary marrow cells. The structure of the nucleus differs from 

 that of the erythroblast. The erythroblasts are not derived 

 each from one of these larger cells by a process of condensa- 

 tion, but the embryonic cells multiply by karyokinesis, and the 

 daughter-cells of the first or following generations acquire the 

 structure of erythroblasts. The chief point in the paper is 

 the proof that the mature nucleated red corpuscles lose their 

 nuclei by extrusion, and not by absorption, in changing to the 

 ordinary red corpuscle of the circulation. The act of extrusion 

 can be observed in part in the living cells. 



6. Very severe and sudden bleeding (in cats) is followed by 

 the appearance in the circulation of red corpuscles containing 

 a large fragment of nuclear material. This fragment persists 

 until the corpuscle disappears. Apparently the greatly accel- 

 erated production of new corpuscles causes a too rapid extru- 

 sion of the nuclei, so that a portion remains entrapped in the 

 corpuscle. 



7. The apparent gemmation of non-nucleated red corpuscles 

 from the nucleated forms, as observed by Malassez, is probably 

 owing to the multiplication of the nucleated cell and the sub- 

 sequent loss of a nucleus from one or more of the daughter- 

 cells before the complete separation of the cells has been 

 effected, 



8. While the spleen of the adult mammal does not take part 

 in the production of new red corpuscles under normal condi- 

 tions, it may be made to resume this function in consequence 



