COMPOSITION OF MAEE'S MILK. 47 



than requisite for the present wants of the blood, and of the 

 living system at large, the kidneys usually take on an increased 

 activity, and soon bring down the dilution of the blood to the 

 proper degree. 



That water passes with extreme rapidity from the stomach 

 of the horse, as from that of mammals in general, is apparent 

 from the well-known fact that a horse will drink within a few 

 minutes a much greater quantity than what his stomach can 

 contain. It is commonly supposed that the excess passes at 

 once into the highest part of the small intestines, namely, the 

 duodenum. But this supposition is hardly necessary, for it 

 is proved that absorption of thin fluids takes place from the 

 inner surface of the stomach with an almost incredible rapidity. 

 This fact is established by many experiments ; and, moreover, 

 that substances dissolved in the water taken in have been found 

 in the urine within an incredibly brief period. The purer the 

 water, the more rapidly is it absorbed partly, perhaps, on the 

 principle of endosmose. That principle is briefly this, that when 

 a texture like an animal membrane is interposed between two 

 fluids which differ in density, the less dense fluid passes freely 

 towards the side where the denser is, while but a small propor- 

 tion of the more dense fluid passes in the mean time to that 

 side on which the less dense fluid is the latter process being 

 called exosmose. 



Mare's Milk. The horse, as everybody knows, is a purely 

 vegetable feeder ; nevertheless, as in mammals universally, the 

 first food of the young animal for some time after it is foaled is 

 an animal fluid, the mare's milk. The average daily increase 

 of a foal during the three months of sucking is upwards of two 

 pounds, being a considerably greater daily increase during this 

 period than after it is weaned. It appears that the average 

 increase of a young horse is 12 per cent in live weight on the 

 amount of food he eats. It may seem at first sight that the 



