CAUSES OF DISEASE. 11 



disease is easily excited in an animal which has been physicked 

 a short time previously. Even a surgical operation will, during 

 the prevalence of an epizootic disease, cause its development in 

 an animal previously healthy. 



Frescnt disease, and conditions bordering on disease. — Diseases 

 of the heart, causing engorgement of the veins, often lead to 

 congestion of the lungs and liver, dropsy of the cavities and 

 areolar tissue ; excessive evacuations, as in diarrhoea and diabetes, 

 predispose to otlier diseases, as glanders or tubercle ; feeble 

 digestive and assimilative powers, to ancemia and dropsies ; 

 inflammations, particularly in horned cattle, to caseous tumours, 

 in parts other tlian those originally inflamed. 



Hereditary tendency. — Many diseases, such as curbs, spavin, 

 ringbones, navicular disease, chorea or stringhalt, run in certain 

 breeds of horses ; tubercle and scrofula in the best breeds of 

 horned cattle. 



Dr. Fleming states that French authors are unanimous in 

 asserting that the disease termed " roaring " in the equine species, 

 and which now generally affects horses in Normandy, was un- 

 known there until the arrival of Danish stallions. 



The influence of climate in overcoming hereditary predisposi- 

 tion is well shown in India, where horses the progeny of roarers 

 are as a rule exempt from this infirmity. 



Diathesis, idiosyncrasy, or aptitude. — Diathesis is a term used 

 to describe a particular tendency to certain forms of disease, 

 such as the rheumatic, tubercular, and scrofulous. In animals 

 of this constitution, the particular disease to which they are pre- 

 disposed, or to which they have a tendency, is caused by 

 different exciting circumstances, and serious diseases are induced 

 by trivial causes, although such animals may present no ex- 

 ternal signs of idiosyncrasy, 



Exopathic predisposing causes. — Wliilst the endopathic causes 

 of disease are generally beyond the influence of our preventive 

 power, those existing external to the animal are to a very great 

 extent subject to our control, and, by a careful study of them, 

 we discover that many diseases are preventible. As a rule, 

 however, extrinsic causes are generally excitants of disease, and 

 it would be a needless repetition if I were to describe them 

 here. I shall therefore pass ou to — 



The exciting causes of disease. — These again present themselves 



