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 Jaminitis 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 lamine, and laminitis is more 
readily induced than congestion or inflammation of the skin or other 
surface organs, because the laminz 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 
