424 HEALTH AND DISEASE 



Cracks in the heel almost invariably run crossways, sometimes extend- 

 ing from one side of the heel to the other, at others being much shorter, 

 when they are situated to the inner or the outer side of the heel just below 

 the fetlocks; or a crack may occur in both positions, or it may be placed 

 lower down in or towards the hollow of the heel. 



Hind-legs and fore-legs alike are subject to this affection, but it is more 

 common in the former than the latter. This difference is probably due -to 

 the facts: (l) that the hind-legs are farther from the 'centre of circulation 

 than the fore ones, and therefore more liable to aggravated attacks of con- 

 gestion and inflammation of the heels; (2) that in badly-regulated stables 

 they are more exposed to moisture -and filth, conditions which contribute 

 so much to the production of the disease. 



Causes. In large numbers of cases predisposing influences play an 

 important part in the cause of cracked heels. In this connection it is 

 noticed that horses of lymphatic temperament, whose limbs are prone to 

 swell from slight disturbing causes, are specially liable to the disease. 



Animals in whom the circulation is enfeebled by age or poverty, and 

 others of a plethoric habit of body, are equally susceptible. 



The exciting causes of cracked heels are such as produce inflammation 

 of the skin, hence it follows upon injuries done by ropes in casting either 

 for operations, or by accident in the stables, and as the result of an exten- 

 sion of inflammation from the foot in certain forms of disease and accident. 



The most common exciting cause, however, is the repeated exposure of 

 the heels to wet and snow during the prevalence of biting easterly winds. 

 Snow when mixed with salt and dirt, as sometimes encountered on the 

 streets of our large towns, is a common inducing cause of inflammation 

 and cracking of the skin of the heels. The disease is also produced by 

 washing the legs in cold weather and leaving them exposed to dry. 



The action of cold and wet in the induction of cracked heels may be 

 stated as follows: Cold, whether it is produced by cold air or the rapid 

 evaporation of water, causes the blood-vessels of the skin to contract, and 

 the quantity of blood circulating in the part is consequently reduced. If 

 the application be continued for a lengthened period, or made repeatedly at 

 short intervals, as when a horse's legs are allowed to become wet again and 

 again and to dry under the influence of cold winds, the contracting power 

 of the vessels is gradually reduced, and sooner or later becomes for the 

 time being exhausted. As a result of this, the pressure of the blood within 

 the vessels begins to assert itself and to overcome their resistance. 



A reaction now sets in, and the vessels which have been caused to 

 contract under the influence of cold open out and become widely dilated 

 and at the same time morbidly distended with blood. This state of things 



