EXTRACT XXX. 



ON KERATOSIS AND HYPERKERATOSIS. 



THE first of these terms seems to us to be applicable to 

 the definition of a natural process always in evidence on 

 the general surface of the skin in greater or lesser degree, 

 and consisting of the formation and exfoliation of horny 

 or epidermal material, the term keratosis being, therefore, 

 used to designate the physiological, while the latter, 

 hyperkeratosis, in like manner applies to the pathological 

 manifestations of the process. 



Keratosis thus used signifies the ordinary proliferation 

 and evolution of the epidermal cell elements, their corni- 

 fication, so to speak, and their final exfoliation from the 

 cutaneous surface as used up and functionless or withered 

 structure. Hyperkeratosis, as thus used, signifies in like 

 manner an exaggerated degree of the natural process of 

 keratosis or the premature cessation of the final stage of 

 exfoliation, by which the local or general accumulation of 

 more or less of the keratosed material is allowed to take 

 place on the epidermal surface, with the result that the 

 involved cutaneous areas are said to be thickened or 

 hyperkeratosed, or to present the pathological conditions 

 known in so many morbid cutaneous processes and diseased 

 states by such names as lepra vulgaris, ichthyosis, etc. 



Keratosis, as a physiological occurrence, is represented 

 by or consists of the conversion of the proliferating dermal 

 into the fully developed epidermal cells, the gradual con- 

 version of these into epidermal scales, and the final 

 shedding of the scales by peripheral exfoliation in regular 

 and uninterrupted structural succession, and, therefore, 



