1 6 ELEMENTS OF HISTOLOGY. [Chap. in. 



of bones (Neumann, Bizzozero, Eindfleisch), in which 

 numerous nucleated protoplasmic cells (marrow cells) 

 are converted into nucleated red blood corpuscles. 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 forma- 

 tion of red blood corpuscles. Again, it is assumed that 

 ordinary white blood corpuscles are transformed into 

 red ones, but of this there is no conclusive evidence. 

 In all these instances the protoplasm becomes homo- 

 geneous and filled with haemoglobin, while the cell 

 grows flattened, discoid, and the nucleus in the end 

 disappears. 



Schafer described intracellular (endogenous) for- 

 mation of red blood corpuscles at first as small haemo- 

 globin particles, but soon growing into red blood cor- 

 puscles, in certain cells of the subcutaneous tissue of 

 young animals. Malassez describes the red blood cor- 

 puscles originating by a process of continued budding 

 from the marrow cells. 



The white corpuscles appear essentially to be 

 derived from the lymphatic organs, whence they are 

 carried by the lymph into the circulating blood. 



CHAPTER III. 



EPITHELIUM. 



17. Epithelial cells (Fig. 13A) are nucleated proto- 

 plasmic cells, forming continuous masses on the surface of 

 the skin, of the lining membrane of the alimentary canal, 

 the respiratory organs, the urinary and genital organs, 

 the free surface of the conjunctiva, and the anterior 

 surface of the cornea. The lining of the tubes and 



