192 EPITHELIAL GLOBULES. 



seated epithelium of this system, the epithelium of the pul- 

 monary vesicles : pneumonia, or inflammation of the lungs, is 

 only an alteration of the epithelium of the vesicles; these cavi- 

 ties are often found filled with fragments of epithelium to such 

 an extent that the air is entirely excluded. Tubercle is hyper- 

 trophy followed by a sort of mummified deposit, formed by the 

 epithelium. This deposit softens after a time, a chemical 

 change similar to that observed in the work of the glands. 



In the intestinal canal, the pathological condition offers us 

 also some important glimpses into the role of the epithelium. 

 Dysentery is a croupous inflammation of this membrane, its 

 morbid product being degenerated epithelium of the large 

 intestine. An intestinal loop in strangulated hernia also 

 exhibits croupous transformation, and this same epithelium 

 also plays the chief part in degeneration of the mucous 

 coat. 



The case is the same with the skin : physiologists for a 

 long time attached no importance to the epidermis, regarding 

 it as a secretory product of the dermis, and yet it is the 

 epidermis which is principally affected in diseases of the skin, 

 and by far the greater number of the diseases called derma- 

 tose are only epidermatose, deterioration of the cutaneous 

 epithelium or epidermis. In producing certain dermatoses 

 artificially, we place the germ of the virulent malady which 

 we wish to ingraft, not in the dermis, but on the surface, or 

 in the depths of the epidermis. In these layers, too, the first 

 signs of most cutaneous diseases appear; these are always, at 

 least in the commencement, only degeneration of the normal 

 product. The elements of epithelial cancerous tumors, how- 

 ever, are in themselves normal; what renders the product 

 morbid in this case is hypertrophy of these elements, an in- 

 crease in number and size. The same remark applies to 

 what are called benign tumors, to corns and callosities, 

 which are all abnormal developments of epidermis; these, 

 meeting with some resistance on the surface, penetrate the 

 interior, breaking through the dermis, the aponeuroses, the 

 tendons, and the muscles, until they reach the bone. Tljose 

 tumors in the integuments, called sebaceous wens, which are 

 at first only as large as the point of a pin, and afterwards 

 often attain considerable size, are also accumulations of 

 epithelial degeneration. 



The vitality and importance of the epithelium are not less 

 striking when we examine that which lines the serous mem- 



