When used, underdrains should be laid from three to four feet below the surface in parallel lines about fifteen feet apart and on grades of not less than one foot in one hundred. It is always better to have the underdrains too large than too small, and drains less than three inches in diameter should not be used, and they should increase in size to four inches and then to six inches as the separate drains are brought together. The writer has seen a six-inch underdrain running full of ground water collected within a distance of a hundred feet, but this was in gravel soil through which the water passed very freely. No exact rules can be given for the size of the underdrains, but it will be noticed that, since water passes through clay soil slowly and through gravel soil rapidly, larger pipes must be used where the soil is coarse. CHAPTER XI _PREPARATION AND CARE OF MILK AND MEAT_ Milk has long been considered to be one of the most important human foods, particularly for the young, combining within itself all the essential elements necessary for the production of cell tissue and for animal vitality. In composition, it is about 87 per cent water, the remaining 13 per cent being divided between fat, casein, and sugar in equal parts, with a small addition of salt. As is well known, milk is the sole food upon which it is possible to sustain life for long periods, and while this applies directly to infants, it is by no means confined to them. Many examples can be given of men and women of mature life who, either on account of some digestive disorder or some mental bias, have confined themselves absolutely to a diet of about two quarts of milk a day and have lived thereon for months and years without suffering from lack of nutrition. In recent years, due to the advocacy of the eminent scientist, Metchnikoff, who asserts that researches in the Pasteur Institute have shown that certain diseases of advanced age are due to auto-intoxication from the larger intestine and that the consumption of fermented milk acts as an antiseptic, neutralizing this bacterial intoxication, the consumption of fermented milk, or buttermilk, or koumiss, has very largely increased. It is, in fact, rather remarkable to find that in large cities, business men whose digestions have been ruined are devoting themselves to unlimited quantities of buttermilk in the hope that their former excesses and absurdities in the way of food may be counteracted and health restored.