IjAMINITIS, OB POXJNDEE. 415 



excessive blood supply, bad shoeing, careless paring of the feet by 

 removing the sole support, and high calkings without corresponding 

 toe pieces must be included under this head. 



Exciting causes. — The exciting causes of laminitis are many and 

 varied. The most common are concussion, overexertion, exhaustion, 

 rapid changes of temperature, ingestion of certain foods, purgatives, 

 and the oft-mentioned metastasis, 



(1) Concussion produces this disease by local overstimulation. The 

 excessive excitement is followed by an almost complete exhaustion of 

 the functional activity of the laminated tissues, the exhaustion by 

 congestion, and eventually by inflammation. But congestion here, as 

 in all other tissues, is not necessarily followed by inflammation ; for, 

 although the principal symptoms belonging to true laminitis are 

 present, the congestion may be relieved before the processes of inflam- 

 mation are fully established. This is the condition in the many so- 

 called cases of laminitis which recover in from twenty-four to forty- 

 eight hours. They should be called congestion of the laminae. 



Laminitis from concussion is common in trotting horses that are 

 raced when not in condition, especially if they carry the obnoxious toe 

 weights, and in green horses put to work on city pavements to which 

 they are unaccustomed. Concussion from long drives on dirt roads is 

 at times productive of the same results, notably when the weather is 

 extremely warm, or at least when the relative change of temperature 

 is great. But the exhaustion of these circumstances must prove an 

 exciting cause as well as the long-continued concussion. This combi- 

 nation of causes must' also determine the disease at times in hunters, 

 for the weight of the rider increases the demands made upon the 

 function of these tissues, and their powers are the sooner exhausted. 



(2) Overexertion, as heavy pulling or rapid work, even where there 

 is no immoderate concussion, occasionally results in this disease; but 

 here also exhaustion is a conjunctive cause, for overexertion can not 

 be long continued without exhaustion. 



(3) Exhaustion is nearly as prolific a source of laminitis as is con- 

 cussion ; for when the physical strength is impaired, even though tem- 

 porarily, some part of the economy is rendered more vulnerable to 

 disease than others. To this cause we must ascribe those cases which 

 follow a hard day's work, where at no time has there been overexer- 

 tion or immoderate concussion. 



The tendency to laminitis in horses on sea voyages results from the 

 continual constrained position the animal maintains on account of the 

 rocking motion of the vessel. 



Where one foot has been bli'stered, or where one limb is incapaci- 

 tated from any cause, the opposite member, doing double duty, soon 

 becomes exhausted, and congestion, followed by inflammation, results. 

 Where one foot only becomes laminitic, it is customary to find the cor- 



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