416 DISEASES OF THE HOKSE. 



responding member participating at a later date; not always because 

 of sympathy, but because one foot had to do the work of two. 



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

 nitis by impairing the normal blood supply. 



This change of temperature may be induced by drinking large 

 quantities of cold water while in an overheated condition. Here the 

 internal 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 cases there has not been sufficient labor per- 

 formed to impair the powers of the laminae, and laminitis is more 

 readily induced than congestion or inflammation of the skin or other 

 surface organs, because the laminae can not relieve themselves of 

 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 pro- 

 tected from this outside influence. In many instances this happens to 

 be some of the internal organs, as the lungs, if 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; secondly, even though 

 these tissues are classed with those of the surface, their protection 

 from atmospheric influences by means of the thick box of horn incas- 

 ing them renders them in this respect equivalent to internal organs. 



A more limited local action of cold may excite this disease, by driv- 

 ing through water or washing the feet and 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 

 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 sim- 

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

 cases of laminitis. 



(5) Why it is that certain kinds of grain will cause laminitis does 

 not seem to be clearly understood. Certainly they possess no specific 

 action upon the laminae, for all animals are not alike affected, neither 

 do they always produce these results in the same animal. Some of 

 these foods cause a strong tendency to indigestion, and the consequent 

 irritation of the alimentary canal may be so great as to warrant the 

 belief that the laminae are affected through sympathy. In other 

 instances there is no apparent interference with digestion nor evidence 

 of any irritation of tlie nmcous membranes, yet the disease is in 



