402 



well as 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 being concussion, overexertion, exhaustion, rapid 

 changes of temperature, ingestion of various foods, purgatives, and the 

 oft-mentioned metastasis. 



(1) Concussion acts as a producer of this disease by the local overstim- 

 ulation which it occasions, the excessive excitement being 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 maybe relieved before the proc- 

 esses of inflammation are fully established. This is the condition that 

 obtains in the many so-called cases of laminitis, which recover in from 

 twenty four tofort3^-eight hours' time. These are the cases which should 

 be called congestion of the laminae. 



Laminitis from concussion is common in track horses trotting races 

 when not in condition, especially if they are carrying 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 undoubtedly the exhaustion so apt to be 

 produced under these circumstances must be considered as exerting 

 almost as great an influence as an exciting cause as does the long-con- 

 tinued concussion. This same combination of causes must also be ad- 

 mitted as determining the disease when seen at times in hunters, for 

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

 function of these tissues, and their i^owers of resisting congestion and 

 its consequences are the sooner exhausted. 



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

 is no chance for Immoderate concussion, occasionally results in this 

 disease, although in the majority of instances exhaustion is a conjunc- 

 tive cause, for overexertion can not be long continued without induc- 

 ing exhaustion. 



(3) Exhaustion, in whatever manner produced, 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 

 after 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 overexertion or immoderate concus- 

 sion. 



