Scheme (After Glucksmann) Illustrating the Relationship Between Cell 

 Division and Cell Differentiation in Different Types of Normal Tissue 



FIG. 1 represents the relatively simple conditions in a hanging-drop preparation 

 of chick fibroblasts tn vitro. The culture presents a form of growth consisting only 

 of proliferating or of potentially proliferating ("resting") cells (magnification X 10). 



FIG. 2 represents condition in the rat embryo where the processes of prolifera- 

 tion and differentiation are separated in lime. Photomicrographs show section 

 through eye of 2-day (left) and 10-day (right) postnatal rat (magnification X 210). 



FIG. 3 represents condition in the eye of the frog tadpole where differentiation 

 and proliferative activity are separated in space, the central parts being fully 

 differentiated and functioning while proliferation still continues in the peripheral 

 region (X 360). (Figure reproduced from Proc. Roy. Soc. Med. 1942, 35, 597.) 



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