34 CYTOMORPHOSIS 



Cytomorphosis includes more than differentiation proper. 

 By continuing it leads to the degeneration of the cell. De- 

 generation appears in many cases to depend upon the trans- 

 formation of the entire protoplasm so that no more true 

 protoplasm remains in the cell. Under such conditions the 

 cells do not remain viable. A good example of this process 

 is afforded by the epidermis, the outer skin, the lowest layer 

 of which consists of undifferentiated cells, which can grow and 

 multiply, Fig. 22. Some of these cells liberate themselves 

 from their parent layer and migrate toward the surface. 

 During their migration their protoplasm is gradually changed 

 into horny substance, and when this change is complete the 

 cells have completed their cytomorphosis and are dead. The 

 surface of our body is covered by dead cells. In this case as 

 in aU similar cases degeneration leads to the death of the cell. 

 We can accordingly distinguish four chief stages of cytomor- 

 phosis. 



1. Undifferentiated or embryonic condition. 



2. Differentiation. 



3. Degeneration. 



4. Death. 



Only in this succession can alterations of cytomorphosis 

 occur, but it must be added that if regressive development 

 should occur it would form an exception to this rule. 



The red blood-corpuscles afford us an excellent example of 

 a complete cytomorphosis. They begin their development 

 as simple cells, with a well formed nucleus but little proto- 

 plasm. Next we observe that the protoplasm grows. Not 

 until it has grown sufficiently does it acquire its character- 

 istic color through the formation of hemoglobin, thus be- 

 coming a young red blood-corpuscle which may still grow a 



