CYTOMORPHOSIS 35 



little, although the nucleus at the same time begins to 

 grow smaller. After the nucleus has become considerably 

 smaller it is separated from the body of the corpuscle. As to 

 how this separation occurs authorities are still disputing. The 

 part left without the nucleus is the so-called mature blood- 

 corpuscle which, however, is not able to maintain its own 

 but soon breaks down. Every day in each of us numberless 

 millions of blood-corpuscles are disappearing. The car- 

 tilaginous cells also pass through a complete cytomorphosis 

 which, when the cartilage is replaced by bone, terminates with 

 the dramatic disappearance of the cells. Cartilage is devel- 

 oped from embryonic mesenchymal ceUs. The cells enlarge 

 and there appears between them the basal substance which 

 imparts to cartilage its characteristic physical consistency. 

 Fig. 8. The so-caUed ossification of cartUage begins with the 

 completion of the chondral cytomorphosis, during which the 

 cells pass through rapid degenerative h3^ertrophy, Fig. 21, 

 which involves the destruction of the basal substance, and 

 which closes with the disintegration, or autolysis, of the cell. 

 Thereupon bone is formed in the place of the cartilage which 

 has disappeared. The nerve cells, at least in vertebrates, 

 pass through their cytomorphosis in a special tempo. Their 

 differentiation advances quite early to the high point at 

 which the cells long remain. The degenerative alterations 

 follow very slowly, so that we usually do not encounter mental 

 weakness in man until advanced age, the weakness being 

 caused by senile atrophy of the brain cells. We are in- 

 debted to the pecuUar course of the cytomorphosis of the 

 brain for the extraordinarily long-lasting functional capacity 

 of this organ. The leaves of plants offer us an excellent 

 example of cytomorphosis. The leaf bud consists of em- 

 bryonic cells which grow and differentiate themselves to 



