CRYSTALLINE LENS g 5 



out the development of its body being thereby impeded. 



The most singular changes occur in small pox. When 



a pock forms upon the bed of the 



nail, there is nothing to be seen 



but a yellowish, somewhat uneven, 



spot ; but if, on the other hand, 



it is developed upon the fold, then 



its traces are left in thfe shape of 



a circularly depressed, and, as it 



were, excavated spot in the body 



of the nail as it gradually advances, ^ 



a proof of a loss of substance pre- / 



cisely similar to that which takes 



place in the epidermis. 



I will not to-day, gentlemen, 

 enter more particularly into the spe- 

 cial history of the formation of epi- 

 dermis and epithelium, although it is of great importance 

 for the right comprehension of many pathological pro- 

 cesses, but content myself with calling your attention to 

 the fact, that, under particular circumstances epithelial 

 cells may undergo a series of transformations, through . 

 which they become extremely unlike what they originally 

 were, and gradually assume appearances which render it 

 impossible for those who are unacquainted with the history 

 of their development to realize their original epidermic 

 nature. The greatest abnormity of the kind is met with 

 in the crystalline lens of the eye, which is originally a mere 



Fig. 17. Diagrammatic representation of a longitudinal section of a nail. a. The 

 normal condition ; a gently curved, horizontal nail, implanted in its fold, and sepa- 

 rated from its bed by a thin cushion, b. A more markedly curved and somewhat 

 thicker nail, with great thickening of the cushion, and much increased curvation 

 of the bed, the fold being shorter and wider, c. Onychogryphosis ; the nail, short 

 and thick, reared up at a considerable angle, the fold short and wide, the bed fur- 

 rowed on its surface, the cushion very thick and composed of layers of loose cells, 

 piled up one above the other. 



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