CHAPTEE I. 



ON THE CAUSES, SYMPTOMS, AND CLASSIFICATION OF 

 DISEASE. 



ETIOLOGY. 



By etiology (a/-/oc, cause, and \<^y^^., law) we mean the 

 science of the causation of disease. 



Etiology is of great importance, it aids our diagnosis, 

 our prognosis, our treatment, and our prophylactic measures. 

 The causes of disease may be divided into intrinsic and 

 extrinsic causes. 

 INTRINSIC CAUSES of disease are : 



1. Heredity.— Offspring may inherit from their parents 

 an actual disease, or they may, as far oftener occurs, inherit 

 a special tendency to various forms of disease. 



2. Age.— Certain diseases are especially characteristic of 

 old age, while others are more liable to attack young 



animals. 



3. Sex.— Besides the diseases arising from the peculiarities 



of the generative organs of the two sexes, it has been 

 observed that sex is of influence in predisposing to certain 

 forms of disease. We may give, as an instance, roaring, 

 which is more common in horses and geldings than m 



mares. 



4. Variety.— Some breeds of animals are more liable to 

 certain diseases than others. As an example, it has been 



