812 VETEEINAEY HYGIENE 



produced by one or other of the definite causes to be 

 referred to. 



The structures implicated in these injuries are skin, 

 muscle, and bone, and we shall first inquire what there is 

 in these which causes them to become affected from either 

 saddle or harness injuries. 



Cause of Injury. — This brings us to a consideration of 

 the actual exciting agents which are at work, and though 

 the list of causes we have to mention is numerous, yet all 

 injuries, slight or severe, and no matter what part of the 

 body they affect, are due to two causes : 



1. Friction. 



2. Pressure. 



If friction be applied to a portion of skin, in a short time 

 the hair is rubbed off and the part becomes covered with a 

 dew of serum, showing that the epithelium has been removed 

 to a sufficient depth to expose the lymph channels. 



If the rubbing be kept on long enough, it will be quite 

 possible to gradually wear a hole in the skin, and expose 

 the tissues beneath ; but it will take longer to wear a hole 

 in the dermis by friction than it will to remove the 

 epidermis. 



The animal most out of condition is the one in which 

 the skin earliest shows the efl^ect of friction, while the 

 animal in the hardest condition is the most resistant. And 

 this holds good for other animals than the horse ; the 

 man trained for a fight is most difficult to bruise or 

 graze. The influence of condition in the prevention of 

 skin injuries, was alluded to in dealing with this subject in 

 an earlier section. In the prevention of injuries by saddles 

 or harness, ' condition ' is of supreme importance ; the 

 most perfectly fitting material will rub an animal that is 

 ' soft,' and this is particularly true of such parts as lie 

 beneath the collar or under the girth, places where con- 

 siderable movement occurs. 



Pressure acts differently ; it produces injury to the skin 

 by depriving it of its capillary blood-supply, and the amount 



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