HORN. 519 



provided by the ridges and furrows of the nail. The upper- 

 most part of the nail, if examined when fresh, is composed 

 of so dense a substance that it is scarcely possible to distin- 

 guish individual cells in it without applying reagents, and at 

 many points an appearance is presented like that which we 

 see in cartilage. But by treating it with potash, we can 

 convince ourselves that this substance is composed of nothing 

 but epidermis-cells/' 



As Virchow justly observes : " From this mode of de- 

 velopment, an easily intelligible distinction may be drawn 

 between the different diseases of the nails," and we might add, 

 of the horse's hoof. The causes of false quarter and seedy-toe, 

 the appearances of canker, are most satisfactorily explained. 

 There is only one of these, affording a useful illustration of the 

 manner in which horn is formed, that we shall rest upon. It is 

 the deformity resulting from the diseased condition hitherto 

 called laminitis, Knollhuf of the Germans, in which a great 

 enlargement occurs at the toe, believed generally to be due to 

 a descent of the os pedis. The change is gradual. From in- 

 flammatory action, a separation occurs between the podophylla 

 (vascular laminse), and keraphylla (horny laminae.) As the 

 inflammation subsides, the space, however small, becomes 

 filled up by the cells which usually agglutinate the horny 

 fibres: but as these are detached, they only become more and 

 more elevated, and the space between the horny wall and the 

 os pedis increases. The toe of the latter becomes atrophied, 

 and it is impossible to obtain a restoration of the wall, be- 

 cause the fibres are pushed outwards by the enormous mass 

 of cells found beneath them. 



There is a disease of the human nail (Onychogryphosis), in 

 every way similar to the above-mentioned deformity of the 

 horse's hoof. Virchow refers to it as follows : " When there 

 is a very abundant development of cells in the bed of the 



