50 THE BIOLOGY OF DAILY LIFE. 



plasm gets homogeneous and of a yellowish 

 colour. All through embryonic life new 

 white corpuscles are transformed into red 

 ones. In the embryo of man and mammals 

 these red corpuscles retain their nuclei for 

 some time, but ultimately lose them. New 

 nucleated red corpuscles are, however, formed 

 by division of old red corpuscles.* Such divi- 

 sion has been observed in the adult blood of 

 certain lower vertebrates (Peremeschko) as 

 well as in the red marrow of mammals (Biz- 

 zozero and Torre). 



" An important source for the new formation 

 of red corpuscles in the embryo and adult 

 is the red marrow of bones (Neumann, 

 Bizzozero, Rindfleisch), in which numerous 

 nucleated protoplasmic cells (marrow cells) 

 are converted into nucleated red blood cor- 

 puscles. The protoplasm of the corpuscle 

 becomes homogeneous and tinged with yellow, 

 the nucleus being ultimately lost. The spleen 

 is also assumed to be a place for the formation 

 of red blood corpuscles. Again, it is assumed 

 that ordinary white corpuscles are transformed 

 into red ones, but of this there is no conclusive 

 evidence. In all these instances the proto- 

 plasm becomes homogeneous and filled with 

 haemoglobin while the cell grows flattened, 

 discoid, and the nucleus in the end disappears. 



" Schafer described intracellular (endo- 



* I venture to question the accuracy of this, the division of 

 red corpuscles has never been observed in the blood of man, and 

 apparently only in the marrow, not blood, of these mammals. 



