44 PHYSIOLOGY AT THE FARM. 



water from the soil : this is their drink. The water so obtained 

 conveys the nutritive matter throughout the plant, and in par- 

 ticular to and from the leaves, where important vegetative 

 operations are performed, and, moreover, preserves that state 

 of moisture throughout the vegetable tissues without which, 

 manifestly, no living function can be carried on. But the water, 

 which is described as the food of plants, has another and a very 

 different office. Under the agency of solar light, it is decom- 

 posed, and supplies its elements, or a part of them, along with 

 the carbonic acid and ammonia of the atmosphere, and the pro- 

 toplasma already existing in the leaves of a living plant, for the 

 production of starch, sugar, albumen, fibrine, and the other 

 proximate principles necessary for the ulterior operations of 

 vegetation, by which products fit for the food of animals are 

 developed. 



Now, it is because there is no evidence of water being de- 

 composed in the animal body for a purpose of the above- 

 described kind that it is refused the name of an aliment in 

 animals, and stationed by itself under the name of drink. And 

 it is to be remembered that many liquids, termed drinks, though 

 they consist of strictly nutritive matter largely diluted with 

 water, are drinks only in so far as they consist of water, the 

 contained organic substance being digested, just as if it had 

 been taken in under a solid form. Thus, physiologically, water 

 is the sole drink of animals. 



But the office which this unchanged water serves everywhere 

 in the animal economy is of the most important character. It 

 was already remarked incidentally that the proportion of water 

 in the body of a living mammal is estimated at four-fifths of its 

 entire weight (p. 6). . This very large proportion of fluid almost 

 takes the animal solids, with the exception of the bones, car- 

 tilages, and hoofs, out of the category of solid parts. In the 

 animal solids, with the exception of those few just enumerated, 



