CAUSES OF DISEASE. 5 



as Ave know, renders women peculiarly susceptible of the con- 

 tagious fevers) is the predisposing cause, the scarlatinal con- 

 tagium is the exciting cause, and the inflammatory processes 

 going on in the skin, tonsils, and elsewhere, the proximate cause 

 of most of the symptoms which the patient manifests. But the 

 exciting cause of the scarlet fever is obviously the proximate 

 cause of that disease, and the proximate causes of its several 

 secondary phenomena are just as obviously their exciting causes." 

 The distinction between the exciting and the proximate causes 

 is thus purely artificial ; whereas tlie differences between the 

 predisposing and exciting causes are generally well marked ; but 

 the co-operation of both of these kinds of causes is, however, 

 generally necessary to produce disease. 



Predisposing causes of disease differ from a 2'>'>^cdisposition to 

 disease. The first may be certain influences operating upon the 

 animal body from without, such as heat, cold, vitiated atmo- 

 sphere, inordinate work, the quality of the food, poisons, &c. ; 

 whilst a predisposition to disease is always intrinsic, existing 

 within the animal body, and is very frequently found to arise 

 from some hereditary taint. For example, horses of certain 

 breeds become roarers, or otherwise defective in their wind, from 

 no appreciable cause. Animals thus affected are said to have a 

 liereditary predisposition to these infirmities. In such instances, 

 the predisposition may be truly said to be the predisposing 

 influence which has given rise to the disease of which roaring or 

 otlier defect in the respiratory function is the symptom ; but it 

 cannot be maintained that a violent inflammation of the larynx 

 or of the lungs, when succeeded by roaring, constitutes a predis- 

 2}osition, although they are most certainly the predisposing, and 

 in some instances the exciting causes of the same pathological 

 condition. 



Predisposing causes of disease commonly consist of various 

 circumstances which influence the functions or structures of the 

 body in an unfavourable manner, yet short of actual disease; 

 or, in other words, those general, non-specific conditions which by 

 their influence so alter the health of the system, or the condition 

 of parts of it, as to render them specially suitable for the develop- 

 ment of certain diseases, provided that an animal so predisposed 

 be subjected to the influence of the excitants of such diseases. 



The exciting causes of disease are those circumstances and 



