356 AMERICAN FARMER'S HORSE BOOK 



walls are very elastic and flexible when in their natural oi 

 healthy state, and expand, to some extent, at every pulsa- 

 tion. But it so happens that they sometimes become grown 

 together and hardened, in which condition they do not ad- 

 mit the flow of blood so freely as before. Ordinarily, no 

 • •' disturbance is noticeable from this change in the coatings 

 of the artery. The duct still appears to be sufficiently large 

 for the passage of the blood, until the horse is severely exer- 

 cised, or otherwise excited ; and then the blood courses 

 * through its channels with such increased rapidity that the 

 diminished capacity of the pulmonary artery is found to be 

 a serious trouble. The vessel does not respond to the grow- 

 ing demands upon it by the heart. The blood now begins 

 to accumulate in the heart, compelling that organ to put on 

 extra labor to urge it forward through the unyielding artery ; 

 and this labored action of the heart often becomes so great 

 that the other arterial channels sympathize with it, and a 

 general throbbing of the internal viscera is the consequence. 

 This throbbing may be plainly seen upon the sides and flanks, 

 and hence the appropriate, though homely, name, thumps. 

 When the excitement passes off, and the blood becomes cooled, 

 and the system tranquilized, these throbbings subside again. 



Thumps affects some horses much more than it does others 

 having the same difficulty, probably from the pulmonary 

 artery being more constricted in such cases. Occasionally it 

 kills the horse. The whole heart sympathizes with, and par- 

 ^ takes of, the disease of the artery, and inflammation is set 

 up, or stricture of the artery takes place. In the latter event, 

 the blood is suddenly stopped, and the horse falls down dead. 



We were once driving a very large, fleshy mare, in a buggy, 

 upon the turnpike leading from Pulaski to Columbia, Ten- 

 nessee. The day was excessively hot. When about mid- 

 way between the two places the mare had an extremely 

 severe attack of this distressing complaint. So violent were 

 the thumpings, that it seemed as if her very sides would be 

 torn asunder. We were compelled not only to stop and rest, 

 but to unhitch her from the buggy. Such terrible throb- * 



