15 



Intermittent pressure or attrition cause hypertrophy ; 

 consta?it pressure, atrophy or absorption. 



Atrophy is the wasting and diminution of a part without 

 change of structure ; but most pathologists include also 

 under the same term such defects of nutrition as result in 

 degenerative changes. 



The causes of atrophy are : 

 Deficient exercise of a part. 

 Deficiency in the supply of blood 

 Defective supply of nervous influence. 

 Inflammation in the part. 



Stimulation and irritation are often inconveniently 

 confounded. It would be convenient and desirable to con- 

 fine the former term to excitation within healthy or normal 

 limits, applying the latter term only to such an excessive 

 action upon a part as produces morbid effects. Irritation is 

 an arrest of a vital movement, in a part, life being considered 

 as a molecular motion. 



Inflammation occurs in connection with so many dis- 

 eases, attacks almost all parts of the animal body, and con- 

 stitutes in one part or another so many of the cases of every 

 day practice, that a correct notion of its general nature and 

 phenomena is of the greatest practical importance. 



The more common and general causes of inflammation 

 are the following : 



Exposure to cold, especially when heated or exhausted, as 

 for example — keeping a horse shivering out of doors to groom 

 him after a long journey. These causes were already treated 

 of in a former chapter, and they need not be repeated here. 

 We may say, however, in passing, that anything that inter- 

 feres with the healthy balance of the circulation, or drives 

 the blood from the skin (or capillary vessels), will cause 

 congestion of internal organs, arrest important sections, de- 

 press vitality, and thus become a fruitful source of many 

 diseases. 



Predisposing causes of inflammation are such as 

 result from peculiarity of temperament, weakened circula- 

 tion from disease, over-work, impure air, deficient nutrition, 

 &c. Exciting or local causes are called irritants ; they may 

 be either mechanical, chemical or vital — these act directly. 

 Other exciting causes act indirectly, such as the introduction 

 of poison into the system, the sudden suppression of dis- 

 charges which are natural or of long standing, the repression 

 of cutaneous eruptions, &c., all of which promote inflam- 

 mation. 



