GENERAL PREDISPOSING CAUSES 31 



The teeth do not perfectly perform their proper function, 

 and the food is passed on in a half-masticated state, and 

 without the requisite admixture of salivary fluid. The 

 digestion is far from being so quick, and a large amount 

 of bulky food is less easily disposed of. The circulation, 

 too, is not so free, in consequence of which there is less 

 gastric juice secreted — often not sufficient — and impaction 

 is the result. 



Here, also, attention may be given to the time occupied 

 in the passage of food through the digestive canal of the 

 horse. 



Henry Jarvis, in 1872, in four experiments, observed 

 the following : 



Horse No. i, fed on oats, performed half an hour's 

 exercise, and passed oats in twenty-four hours. 



Horse No. 2, fed on oats, performed a nine miles' 

 journey, aiid passed oats in twenty-two hours. 



Horse No. 3, fed on oats, kept quiet in stable, and 

 passed oats in twenty-seven hours. 



Horse No. 4, fed on oats, kept quiet in stable, and 

 passed oats in twenty-seven and a half hours. 



These periods, I need hardly add, are comparatively 

 short, and the average time has been estimated by other 

 authors to be nearly four days. In either case the time 

 is wonderfully short. This fact must be remembered in 

 close connection with another : I refer to the nature of the 

 horse's food. We know quite well that a very great pro- 

 portion of his provender is of an indigestible nature, and 

 that a very large amount of the material taken into his 

 body is excreted unchanged. We know equally well that 

 this excretion is going on with almost mathematical 

 regularity throughout the day. In other words, the 

 horse in health requires to empty his rectum eight to 

 ten or twelve times during every twenty-four hours. 



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