The =legal limits= of dilution of whiskey, brandy and rum is down to 25 degrees under proof, and of gin down to 35 degrees under proof. (For definition of proof spirit, see page 55). The amount of alcohol in an alcoholic liquor is determined by distillation of 100 c.c., making up the distillate to 100 c.c. by the addition of distilled water, and then taking the specific gravity of a portion of this liquid by the aid of the specific gravity bottle. The percentage of alcohol corresponding to a given specific gravity is given in tables prepared for this purpose. Prolonged indulgence in spirits produces the various organic diseases already described, and unless well diluted they are more harmful than beers or wines. They differ from wines and beers in not tending to produce gout, and from beer in not leading to obesity. CHAPTER IX. WATER. =Uses of Water.=—Water is a prime necessity of life. In its absence life can only exist in lowly organised beings, and in them only in a dormant state. From a hygienic point of view, the uses of water are four-fold:—(1) It is =an essential part of our food=, not only serving to build up the tissues of the body, but also preserving the fluidity of the blood and aiding excretion of effete matters. (2) It is necessary for =personal cleanliness=, of which the importance can scarcely be exaggerated. (3) =In the household= it is essential for cooking, as well as for washing the house, the linen, and various utensils. (4) By =the community at large= it is required for water-closets and sewers, for public baths, for cleansing the streets, and for horses and other domestic animals, as well as in many manufacturing processes. It is obvious that the water to be used for domestic and general purposes, need not be so pure as that for drinking purposes. Hence, a double supply was proposed for London in 1878, by the Metropolitan Board of Works—a less pure river supply for general purposes, and a deep chalk-well supply for drinking purposes. The scheme, however, rightly fell through, because of the expense of a double source of supply, and the danger that the impure water would, through carelessness or ignorance, be often used for drinking purposes, when it happened to be nearest at hand.