KERATOSES. 359 



by the fact that the stratification of the horny cells of tlie 

 epidermis follows a different law from that by which it is 

 normally governed. 



It is well known that under ordinary conditions, the strata 

 of homy cells lie parallel with the surface of the bod}-, and 

 that the papillae take no part in the finer subdivision of the 

 cutaneous surface. It is only the deepest layer of cells forming 

 the rete Malpighii, which accurately follows every elevation and 

 depression; and which would therefore present, if taken by 

 itself, a perfect mould of the papillary body. Between this and 

 the horny layer is interposed the thick cushion of the " inter- 

 mediate cells;" these are not stratified, and therefore furnish 

 materials which are, from this point of view, quite neutral, for 

 filling up all the inequalities of the layer below them, and so 

 paving the way for the horizontal stratification of the layers above 

 them. In the keratoses these "intermediate cells" are either 

 quite absent or else disproportionately few in number. To the 

 best of my belief they become prematurely horny, and this I 

 regard as the essential physiological basis of the entire disorder. 

 The absence of "intermediate cells" necessarily entails the 

 absence of any transition from the one plane of stratification to 

 the other : the horny layer of the epidermis is obliged in conse- 

 quence to follow the rete Malpighii in its adaptation to all the 

 elevations and depressions of the papillary body. Eacli layer 

 of horny cells must therefore send into the layer which lies 

 immediately above it, processes exactly resembling those which it 

 receives from the layer immediately below it ; processes which 

 correspond exactly to those which the papillary body projects 

 into the deepest laj- er of the horny stratum. All the constituent 

 layers are thus indissolubly united ; hence all the horny matter 

 remains where it is produced ; hence too the possibility of those 

 extraordinary thickenings of the horny lamina which charac- 

 terise the entire group of keratoses. 



§ 304. Following Lehert^ we distinguish a diffuse from a cir- 

 cumscribed form of keratosis. The former results in the pro- 

 duction of flat, horny scales, which often cover large areas of 

 skin. Not unfrequcntly they resemble the scales of fishes ; hence 

 the name Icldhyosls; occasionally tlicy assume a more protuberant, 

 conoidal or prismold form, thus approaching the circumscribed 

 variety of keratosis, the cornu humavum. That the great bwlk 



