DISEASES OF THE HORSE. 415 



the functional activity of , the laminated tissues, the exhaustion by con- 

 gestion, 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 pre's- 

 ent, the congestion may be relieved before the processes of inflamma- 

 tion 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 laminte. 



Laminitis from concussion is common in track horses trotting races 

 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 unaccastomed. Concussion from long drives on dirt roads is 

 at times productive of the same results, notabl}^ 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 tendenc}^ 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 blistered, or where one limb is incapacitated 

 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 correspond- 

 ing member participating at a later date; not alwa3\s because of S3'm- 

 pathy, 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 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. 



