442 DISEASES OF THE HORSE. 



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 concus- 

 sion. This combination 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 when there 

 is no immoderate concussion, occasionally results in this disease. 

 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 

 concussion, for when the physical strength is impaired, even though 

 temporarily, 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, in which at no time has there been 

 overexertion 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. 



If one foot has been blistered, or if one limb is incapacitated from 

 any cause, the opposite member, doing double duty, soon becomes 

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

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

 sponding 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 

 laminitis 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 lamin?e 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 



