190 DISEASES OF THE FEET. 



than the hind, and are not so frequently moved when the horse is 

 standing, generally one or both of these feet are alone implicated 

 in an attack of laminitis, whether the disease proceeds from con- 

 gestion or from injury. 



NATURE OF THE DISEASE.— The whole body of the horse 

 (like that of a man) is covered by a membrane which acts as a 

 filter for the removal, from the body, of wa.tery fluid and waste 

 products contained in it. Thus, in the lungs, it gives off water 

 and carbonic acid ; and on the surface of the body, principally 

 water in the form of perspiration. The kidneys, which are a 

 peculiarly modified portion of this covering, discharge urine. 

 Besides its office as a filter, it has the power, to a certain extent, 

 of altering the composition of the waste material passing through 

 it, chiefly as a protective layer, in the form of epithelium (p. 154) 

 which assumes^ special characters according to its position. Thus, 

 the true skin excretes scarf-skin (p. 154) and hair; and the 

 membrane which covers the sensitive parts of the foot, secretes 

 horn. At the coronet, the horn-producing membrane excretes 

 the wall of the hoof; on the outer surface of the pedal bone (Fig. 

 70, p. 209) it excretes soft horny cells which bind it (the sensitive 

 laminae) to the wall ; and underneath the foot it excretes the sole 

 and frog. 



The growth of this protective covering (epidermis) is dependent 

 on the amount of serum (watery portion of the blood) which 

 accumulates inside the secreting membrane. Hence, the slower 

 the superficial circulation, the thicker will be the protective 

 covering. Thus, the oolder the climate, the more developed are 

 the hair, hoofs, and horns of animals which live in it. A blister 

 and pressure (as in the case of corns from tight boots) increase 

 epidermal growth in a similar manner. Comparative stagnation 

 of blood plays its part as the epidermal stimulant in " filled " legs, 

 grease, human tuberculosis (consumption), and diseases of the 

 heart. The fine and scanty coats of horses which are warmly 

 clothed, well exercised, and vigorously groomed, or inhabit hot 

 climates, show the effect that increased superficial circulation has 

 in dirninishing epidermal growth. Certain high fevers in man 

 also cause loss of hair. 



The abnormally large amount of horny matter excreted by the 

 sensitive laminae in cases of acute laminitis, is undoubtedly due 

 to congestion or stagnation of blood, and not to inflammation. 

 " Dropped sole " is caused by the rapid secretion of this new 

 horn, which, being continually secreted, exercises enormous 

 pressure between the hoof and the ^edal bone, and finally forces 

 the point of the bone down and reduces the slope of the hoof. 



