FOOD 



87 



tanks are now made for fixing at the highest points of drains, and can lie 

 regulated to discharge a fixed quantity of water periodically — (say) once 

 or twice a day. They require no attention, except for cleaning and repairs, 

 and are useful for keeping drains clean, particularly in flat districts where 

 the drains are laid with very little fall. The automatic flush-tanks may 

 be supplied from an overhead rain-water tank, but a supplementary supply 

 of water should be laid on for use in dry weather. 



FOOD 



Nutrition may be defined as the process by which the waste which 

 is constantly going on in the animal's system is compensated by the 

 deposit of fresh material derived from food, solid and liquid. To under- 

 stand exactly what is required it is necessary to know something of the 

 constitution of the body, and it may be stated, in the first instance, that 

 four elementary substances, oxygen, hydrogen, carbon, and nitrogen, are 

 the principal constituents of the important tissues of the animal body, 

 muscle, nerve, and the solid particles of the blood. 



Constitution of the Body. — Organic bodies include albuminoids or 

 proteids, gelatine, horny matter, and fats (composed of carbon, oxygen, and 

 hydrogen, nitrogen being absent). All these constituents are combustible. 

 Besides the combustible constituents there is a considerable proportion 

 of incombustible, and when burned with those which are combustible they 

 are left as ash, of which bone ash forms the largest proportion. Bone ash 

 consists chiefly of phosphate of lime and magnesia, with a small quantity 

 of the carbonate. The ash obtained from the burning of muscle or flesh 

 contains a considerable proportion of the phosphate of potassium. The 

 whole of the constituents of the animal body are combined with a very 

 large proportion of water, which, however, varies in different animals, and 

 at different ages, from a little over 40 per cent to nearly 70. The follow- 

 ing table will show the proportion of water, nitrogenous matter, fat, and 

 ash in the bodies of cattle, sheep, and pigs : — 



Percentage Composition of Whole Bodies of Animals 



