HISTORY AND CAUSES OF DISEASE. 41 



be so circumstanced as to acquire predisposition. A horse 

 may inherit from its dam or sire a predisposition to ophthal- 

 mia, to roaring, and to various other diseases ; or it may 

 manifest, in the narrow make of its chest, an inclination to 

 pulmonary disorders ; or in the sickle-like bend of its hocks, 

 a disposition to curbs. Take a colt out of its native fields, 

 place it in a warm stable, and feed it well, and you 

 predispose it to all sorts of inflammatory affections : you 

 render it 'plethoric, and plethora (as has been already 

 shown) is a condition verging upon disease. 



In the course of our observation, we note two kinds of 

 predisposition : — a healthy and an unhealthy predisposition ; 

 which may either pre-exist independently of each other, or 

 may be engrafted one upon the other. To explain this, I 

 will suppose several horses of tender ages to be pent up in 

 warm stables, put to work, and fed accordingly : some of 

 these will get colds ; some inflammation of the lungs ; some 

 swelled legs ; some farcy ; some glanders ; some ophthal- 

 mia, &c. In all, the same exciting cause has been ope- 

 rating, and under the same circumstances : we can only 

 explain the different result by asserting the predisposition 

 has been different. We will suppose, however, that one of 

 these horses having an attack of swelled legs is worked on : 

 the case, which was but swelled legs, now turns into one of 

 farcy. We may account for this by supposing, either that 

 an unhealthy predisposition has become engrafted upon an 

 originally healthy body ; or by saying, that the intensity of 

 the exciting cause has been such as to create malignant effects. 

 I knew a horse — a farmer^s riding horse — which, after 

 having been hunted, and returned to his stable, tired and 

 over-marked, exhibited on the following day swelling of all 

 four legs, in combination with signs of a highly nervous 

 excitement : at the end of a week the animal was shot for 

 having become virulently farcied and glandered. 



Exciting Causes are such as, when applied to the body, 

 excite the disease. A blow, a burn, a blister, inoculation, 

 the atmosphere of a foul stable, are all exciting causes. In 

 nature, therefore, it is obvious there are but two kinds of 



