32 



CYTOMORPHOSIS 



cellular spaces. It is not practicable to lay further illustra- 

 tions before you. 



Progressive development is closely connected with another 



phenomenon. The 

 embryonic tissues 

 grow with immense 

 rapidity, the differen- 

 tiated tissues on the 

 contrary grow slowly. 

 If we investigate the 

 conditions more care- 

 fully we learn that the 

 ceUs gradually lose 

 the power of division 

 as they are differen- 

 tiated. If the differ- 

 entiation progresses 

 far, then probably the 

 capacity of division is 

 lost to the cells alto- 

 gether. Formerly we 

 had no exact concep- 

 tion of the rapidity of 

 growth in embryos. 

 This is a question 

 about which I have 

 been greatly interested 

 for many years. In 

 the book "The Prob- 

 lem of Age, Growth 

 and Death," which I 

 published in 1908, I 



Fig. 19. — Nerve cell from the spinal cord of 

 man. The Nissl bodies have been dissolved out 

 and the cell so colored that the neurofibrils are 

 brought out. fi, fibrils; x, fibrils in a dendrite; ax, 

 nerve fiber; lii, space left by the dissolving of the 

 Nissl bodies; ke, nucleus. — From K. C. Schneider, 

 after Bethe. 



