2o6 THE HORSE. 



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 influence. In many instances this happens 

 to be some of the internal organs, as the lungs, where the previous work 

 has been rapid and their activity impaired; but in numerous other in- 

 stances the blood is forced toward the feet, and that it so depends upon 

 two facts; first, that these tissues have been greatly excited and are 

 already receiving as much blood as they can accommodate consistently 

 with health; secondly, even though these tissues are classed with those 

 of the surface, their protection from outside influence by means of the 

 thick box of horn around them renders them in this respect equivalent to 

 internal organs. 



Again, a 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 reaction takes place 

 in the surface tissues of the limbs, and passive congestion of the foot re- 

 sults 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 

 or congestion, soon to recover, yet they may become true cases of 

 laminitis. 



2 . Over-exertion. Heavy pulling or rapid work, even when there is 

 no change for immoderate concussion, occasionally results in this disease, 

 although in the majority of instances exhaustion is a conjunctive 

 cause, for over-exertion can not be long continued without inducing 

 exhaustion. 



3. Exhaustion. However produced, this is nearly as prolific a 

 source of laminitis as is concussion, for when the physical strength has 

 been greatly impaired, even though but temporarily, some part of the 

 economy is rendered more vulnerable to disease than others, and it is 

 not strange that in many instances it should be those parts still 

 called upon to perform their function of maintaining the weight of the 

 body and their activity has been exhausted. It is to this cause we 

 must ascribe those many cases which we see following a hard day's 

 work, where at no time has there been over-exertion or immoderate 

 concussion. 



The same cause exists where one foot has been blistered, or where one 

 limb is incapacitated from any other reason; for the opposite member 



