DRINKING. 75 



prehension of food in a manner somewhat similar to that done 

 by the upper lip of a horse. 



DRINKING. 



In drinking, the action of the mouth is that of a suction 

 pump, in which the tension of the air in the mouth is reduced 

 by the tongue being drawn back while the lips are kept 

 closed. If this is done while the horse's muzzle is immersed 

 in the fluid and the lips are separated without any air being 

 admitted, the fluid will rush into the mouth and will rise 

 to a height sufficient to render the pressure of the fluid on 

 the air in the mouth equal to that of the atmosphere, and 

 also sufficient for the swallowing muscles to force the fluid 

 into the gullet. In this process, the action of inhaling 

 (drawing in the breath) appears to have little or no effect ; 

 for we find that a horse which has an open tracheotomy 

 tube in his windpipe will drink as easily as a sound horse, 

 other conditions being equal. In drinking, a horse naturally 

 keeps his nostrils above the surface of the fluid, as he has 

 to breathe through them ; but while his nostrils are un- 

 immersed, the corners of his mouth will also be above the 

 surface of the fluid. Hence, if the lips are separated at their 

 corners, as for instance by the wearing of a curb bit, and 

 especially if the reins are drawn more or less tightly, the 

 animal will be greatly impeded in drinking, even if he is not 

 altogether prevented from swallowing the fluid. A snaffle 

 is less liable to cause interference in this manner than a 

 curb ; because it is as a rule put lower down in the mouth, 

 and if jointed, it hangs down by the bending of its joint, 

 and does not draw the lips apart so much as the mouthpiece 

 of a curb would do. 



According to Colin, a horse when drinking, takes from 

 .26 pint to .44 pint at each " go-down " (swallow), and drinks 

 at the rate of from 65 to 90 go-downs a minute. The 



