COMMON DISEASES OF 

 FARM ANIMALS 



CHAPTER I 

 GENERAL DISCUSSION OF DISEASE 



Disease is the general term for any deviation from the 

 normal or liealtliy condition of the hody. The morbid processes 

 that resnlt in either slight or marked modifications of the normal 

 condition are recognized by the injurious changes in the struct- 

 ure or function of the organ, or group of body organs involved. 

 The increase in the secretion of urine noticeable in horses in the 

 late fall and winter is caused by the cool weather and the decrease 

 in the perspiration. If, however, the increase in the quantity 

 of urine secreted occurs independently of any normal cause and 

 is accompanied by an unthrifty and weakened condition of the 

 animal, it would then characterize disease. Tissues may undergo 

 changes in order to adapt themselves to different environments, 

 or as a means of protecting themselves against injuries. The 

 coat of a horse becomes heavy and appears rough if the animal 

 is exposed to severe cold. A rough, staring coat is very common 

 in horses affected by disease. The outer layer of the skin be- 

 comes thickened when subject to pressure or friction from the 

 harness. This change in structure is purely protective and 

 normal. In disease the deviation from normal must be more 

 permanent in character than it is in the examples mentioned 

 above, and in some way prove injurious to the body functions. 



Classification. — We may divide diseases into three classes: 

 non-specific, specific and parasitic. 



Non-specific diseases have no constant cause. A variety of 



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