58 DISEASES OF THE HOESE'S FOOT 



locking of the sensitive and horny laminse. We see that 

 the horny laminae are ingrowths of the rete Malpighii, 

 ploughing into and excavating the corium into the shape of 

 leaves — the sensitive laminae. Putrefactive changes simply 

 break into two separate portions what originally was one 

 whole, by destroying the cells along its weakest part. This 

 part is the line of soft protoplasmic cells of the rete 

 Malpighii. Thus the more resistant parts (the horn on the 

 one hand, and the corium covering the foot on the other) 

 are easily torn asunder. 



As a result of the evidence we have quoted, w'e are able 

 to answer our original question in the affirmative. Seeing 

 that the horny and the sensitive laminae are both portions 

 of the same thing — namely, a modified skin, in which the 

 epidermis is represented by the horny laminae, and the 

 corium by the sensitive — it is clear to see that the cells 

 covering the inspreading horny laminae are dependent for 

 their growth and reproduction upon the cells with which 

 they are in immediate contact — namely, those of the sensi- 

 tive laminae — and that therefore the sensitive laminae are 

 responsible for the growth of the horny. 



B. CHEMICAL PROPEETIES AND HISTOLOGY OF HORN. 



Horn is a solid, tenacious, fibrous material, and its 

 density in the hoof varies in different situations. It is 

 softened by alkalies, such as caustic potash or soda and 

 ammonia, the parts first attacked being the commissures, 

 then the frog, and afterwards the sole and wall. Strong 

 acids, such as sulphuric acid and nitric acid, also dis- 

 solve it. 



The chemical composition of the hoof shows it to be 

 a modification of albumin, its analysis yielding water, a 

 large percentage of animal matter, and materials soluble 

 and insoluble in water. The proportions of these, as existing 

 in the various parts of the hoof, have been given by 

 Professor Clement as follows : 



