410 CHEMISTRY. 



Such are the " buffalo-licks " of this country. The results 

 of some experiments which have been tried with cattle in 

 relation to salt as an article of food are interesting and 

 instructive. The salt had no influence on the flesh or on 

 the amount of milk obtained ; but the set which had salt 

 mixed with their fodder had a much better coat, and were 

 much more lively than the set from which salt was with- 

 held. 



581. Water. This is the largest ingredient in animal 

 bodies. It constitutes nearly 80 per cent, of the blood, and 

 the same of the brain, and nearly 75 per cent, of the muscles. 

 The body of a human being is about three fourths water. 

 One great use of this abundant substance in the animal is 

 to furnish a proper vehicle for the solid substances in their 

 circulation. The materials for growth are carried every 

 where in it, and the worn-out particles are conveyed to their 

 natural outlets. It also serves various purposes in the tis- 

 sues, giving transparency to some, as the cornea, the beau- 

 tiful clear front-covering of the eye, and giving to the mus- 

 cles and the membranes their softness, flexibility, and elas- 

 ticity. Water is in these respects as essential to life as any 

 other substance. Being thus needed in the animal, it is 

 largely present in all the vegetable substances which are 

 used as food ; and as in vegetables it furnishes in its 

 decomposition its elements for the formation of the com- 

 pounds which they contain, so it may do to some extent 

 in animals. 



582. Endosmose and Exosmose. In connection with water, it is 

 proper to notice an agency which has a wide influence on the circulation of 

 matter, both in vegetable and animal substances. This agency is exhib- 

 ited in the following experiment: B C (Fig. 119, p. 411) is a glass tube 

 expanded at its lower end, which has a piece of moist membrane, as fresh 

 bladder, tied over it. If we pour some water into the vessel, and also so 

 much into the tube as will make it at the same level with that in the vessel, 

 there will be no change in the levels, however long the apparatus mny be left 



