72 



HOWELL. [Vol. IV. 



puscles spring from colorless cells found in the blood-forming 

 organs ; but these colorless cells are not the white corpuscles 

 of the blood, indeed never under normal conditions get into the 

 circulation. 



The most important discovery of the century with reference 

 to the development of the red corpuscles was made simultane- 

 ously and apparently independently by Neumann {^a) and by 

 Bizzozero {ic^a). In 1868 these observers found that in the 

 red marrow of the bone nucleated red corpuscles occur, which 

 are similar to those found in the embryo, and that they are pres- 

 ent throughout the life of the animal. A nucleated red corpus- 

 cle can only be interpreted as the predecessor of a non-nucleated 

 red corpuscle, and the discovery therefore meant that the red 

 marrow of the bones is an organ for the production of new red 

 corpuscles throughout extra-uterine life. In his first papers 

 Neumann spoke of the nucleated red corpuscle as being de- 

 rived from colorless lymphoid cells, and described transitional 

 forms ; but in his later papers he does not lay so much stress 

 upon the transitional forms, while still believing without 

 doubt that the red cells are derived from colorless ones. With 

 reference to the change from the nucleated red corpuscle to 

 the ordinary form, he agrees practically with Kolliker's view 

 of the nature of this change in the embryo. The loss of the 

 nucleus takes place by a process of absorption within the cell, 

 and may be preceded by fragmentation. Neumann (5//) be- 

 lieves that in the adult the bone marrow is the sole organ for 

 the production of new red corpuscles, and gives a number of 

 experiments to prove that the spleen takes no part in their 

 formation, either under normal conditions or after severe hem- 

 orrhage. Bizzozero also found the nucleated red corpuscles in 

 the marrow, and afterwards showed that these cells are capa- 

 ble of multiplication by indirect division. This latter obser- 

 vation has been confirmed abundantly by later investigations, 

 and makes a second important step in our knowledge of the 

 origin of the red corpuscles. Bizzozero placed too much weight 

 apparently upon this growth of the nucleated red corpuscles, 

 and overlooked the importance of the colorless cells from which 

 the red corpuscles arise. The nucleated red corpuscles of the 

 marrow are derived, he thinks, from the similar embryonic 

 cells occurring in the liver and spleen during foetal life. When 



