416 



find the other or corresponding menil)er participating at a later date, 

 not always because of sympathy, but because the transfer of all the 

 functional performance to the one foot proves within itself a sufiacient 

 exciting cause. 



(4) Rapid changes of temperature act as an exciting cause of lami- 

 nitis in precisely the same way as they act to produce disease in other 

 tissues, the result of these variations of temperature showing itself 

 upon those parts rendered particularly susceptible to pathological 

 changes from some impairment of their natural disease-resisting 

 powers. 



This change of temperature may be induced by drinking large quan- 

 tities of cold water while in an overheated condition. Here the inter- 

 nal heat is rapidly reduced, the neighboring tissues and blood-vessels 

 constrained, and the blood supply to these organs greatly diminished, 

 while the quantity sent to the surface is correspondingly increased. 

 True, in many of the cases which result from this cause there has not 

 been sufficient labor performed to impair the powers of the lamiufe, 

 and I am inclined to the opinion that laminitis is the more readily 

 induced than congestion or inflammation of the skin or other surface 

 organs because of the impossibility upon the part of the lamina3 to 

 reUeve themselves of the threatened congestion by the general safety- 

 valve of perspiration. A cold wind or relatively cold air allowed to 

 play upon the body when heated and wet with sweat has virtually the 

 same result, for it arrests evaporation and rapidly cools the external 

 surface, thereby determining an excess of blood to such organs and 

 tissues as are protected from this outside i nfluence. In many instances 

 this happens to be some of the internal organs, as the lungs, where the 

 previous work has been rapid and their functional activity impaired; 

 but in numerous other instances the determination is toward the feet, 

 and that it is so depends upon two very palpable facts; first, that 

 these tissues have been greatly excited and are already receiving as 

 much blood as they can accommodate consistently with health; sec- 

 ondly, even though these tissues are classed with those of the surfac4, 

 their protection from atmospheric influences by means of the thick 

 box of horn incasing them renders them in this respect equivalent to 

 internal organs. 



Again, a still more limited local action of cold excites this disease, 

 as seen from driving through water or washing the feet or legs while 

 the animal is warm or just in from work. Here a very marked reac- 

 tion takes place in the surface tissues of the limbs, and passive con- 

 gestion of the foot results from an interference with the return flow 

 of blood, which is being sent to these organs in excess. These are 

 more apt to be simple cases of congestion, soon to recover, yet they 

 may become true cases of laminitis. Youatt says: "The danger is 

 not confined to the change from heat to cold; a sudden transition 

 from cold to heat is as injurious, and therefore it is that so many 



