DISEASE IN GENERAL 139 



dissemination of disease in large stables. Attention was called to 

 the air requirements of the body in the chapter on Respiration. 

 An adequate ventilating system should be provided in the stable 

 to insure a supply of fresh air at all times. 



Exercise, when excessive, leads to fatigue and tissue destruc- 

 tion. Lack of exercise interferes with the blood-supply and 

 nourishment in all parts of the body, and predisposes to azoturia, 

 swollen legs, colic, etc. 



Work plays a part in acquiring disease. Horses which are 

 worked in places where many impurities exist in the atmosphere 

 are subject to bronchitis, pneumonia, and other diseases of the 

 respiratory organs. Draft horses used for years on the pavements 

 of city streets acquire a predisposition to certain forms of lameness. 



Auto-intoxication is a self-poisoning due to an accumulation of 

 poisonous substances in the body. In most cases irregularities in 

 digestion or elimination are responsible. When the digestive sys- 

 tem fails to dispose of the by-products promptly, they are absorbed 

 and act as poisons to other organs. The kidneys, which normally 

 throw off certain waste products, are placed under too great strain. 

 This results in an inflammation of the mucous membrane lining 

 their tubules and interferes with their function. In the horse, 

 azoturia is a notable example of auto-intoxication. Proper feed, 

 care, and exercise will prevent and relieve this serious affection. 



(B) Determining causes of disease are those that operate di- 

 rectly to produce disease. They act more efSciently if some pre- 

 disposing cause has first been operative. In fact, it is doubtful if 

 predisposing causes in moderate action and without too great 

 persistance are capable of producing a distinct anatomic or func- 

 tional fault of sufficient importance to be termed "disease." How-, 

 ever, if the cause persists in operating it is certain to lead to actual 

 disease. Determining or exciting causes of disease deserving men- 

 tion are traumatisms, poisons, and parasites. 



Traumatisms are any form of injury which produce lesions or 

 wounds in the tissues of the body. They will be more fully dis- 

 cussed in the chapter on Wounds. 



Poisons are substances that destroy life or impair the func- 

 tions of one or more of the body organs. They may be separated 

 into three classes, as follows — (1) animal poisons, like snake venom, 

 which is highly toxic; (2) vegetable poisons, Hke opium and strych- 

 nin; (3) mineral poisons, like arsenical salts, caustic soda, silver 



