RETROGRIiSSIVE TISSUE CHANGES. 



225 



epithelium and stimulates the formation of excessive quantities 

 of cellular cement favors keratosis. 



Appearance. — Macroscopic. — Keratotic accumulations appear 

 like so much irregularly formed horn tissue. The resistance 

 of the cornified epithelium varies according to the completeness 

 of cornification. 



4. 



-> . :iV\ 



Fig. 119. — Photograph ot a Keratotit, liorn-like growth removed from 

 region of withers of an ox. 



Microscopic. — The cornified epithelium usually appears as 

 a mass of debris, although in some instances there may still be 

 evidence of cellular elements. The epithelial pearls of epitheli- 

 omata probably represent a type of keratosis, — the pearls appear- 

 ing as whirls of scale like elements suggesting the gross appear- 

 ance of a section of an onion. 



Tissue Affected.— Epithelium is particularly affected. Some 

 tumors are affected, especially epitheliomata. 



Effects. — The area involved is inconvenienced. If the en- 

 tire skin is involved there may be secondary constitutional les- 

 ions. 



