tilizers. Yet in most cities all the waste is either burned and destroyed or freighted out and dumped into the sea or some large body of water. It was calculated by a former street-cleaning commissioner in the old city of New York (now the Borough of Manhattan) that the dry refuse reached the aggregate of 1,000,000 tons annually and the garbage 175,000 tons annually. The value of the salvable part of this great mass of waste was stated to be over $650,000 a year. Sanitation is concerned with the disposal of garbage. See Garbage and Refuse Disposal; Sewage Disposal; Plumbing.
Prevention of Disease. This is a large question, on which this article can only briefly touch. Much depends upon knowledge of the ætiology or the remote causes of disease. The best rule for preventing disease is to follow out carefully the principles of general hygiene (q.v.) with reference to pure air, pure water, proper food, cleanliness, etc. Provision may be made against certain diseases. Malaria (q.v.) may be prevented by destroying mosquitoes and depriving them of their breeding places, as well as by screening doors and windows of houses in malarious districts. Smallpox may be prevented by persistent revaccination. (See Vaccination.) Typhoid fever may be prevented by boiling all water before it is drunk or used in cooking, by cooking oysters thoroughly, by most scrupulous drenching of all raw vegetables which may have been watered with liquid manure, and by preventing insects from gaining access to typhoid patient's dejecta or clothing before thorough disinfection has been practiced. (For the diseases transmitted through the agency of insects most of them preventable, see Insects, Propagation of Disease by.) In most large cities compulsory notification to the Board of Health is legal in the case of cholera, yellow fever, plague, smallpox, chicken-pox, diphtheria (including membranous croup), typhus, typhoid, tuberculosis, measles, and spotted, relapsing, and scarlet fevers, all of which are considered contagious except typhoid. Isolation is practiced in all these diseases, partial or absolute. Much stress has been laid upon disinfection as a means of preventing disease, and if properly carried out it has some efficiency. But it is a mistake to place too implicit reliance upon it as ordinarily practiced. See Disinfectants.
The Disposal of the Dead. In order to understand the importance of this subject one must know something of the changes which the body undergoes after death. A body that has been buried gradually breaks up into a large number of comparatively simple compounds, such as carbonic acid, ammonia, sulphureted and carbureted hydrogen, nitrous and nitric acid, and certain more complicated gaseous matters with a very fetid odor, which finally undergo oxidation; while the non-volatile substances usually enter into the soil, and either pass into plants or are carried away by the water percolating the soil. These changes are accelerated by the worms and other low forms of life that usually swarm in decomposing bodies; and the character of the soil materially influences the degree of rapidity of destruction. The bones remain almost unchanged for ages. If a body is burned, decomposition is incomparably more rapid, and different volatile combinations may arise, the mineral salts and a little carbon alone remaining. Putting aside the visionary schemes for turning the dead to commercial account, there are three methods of disposing of our dead for consideration, viz. burial in land or in water, or cremation. At present the question is not urgent; but it may become so in a century or two, if the population continues to increase at the present rate. Even in our own time a great change has taken place, and the objectionable habit of interments in and around churches in towns has been abandoned, cemeteries in the country being now commonly employed, except in the ease of country villages. The air over cemeteries is, however, always contaminated, and water percolating through them is unfit for drinking purposes. The evils are lessened by making the grave as deep as possible, and by placing not more than one body in one grave. Plants should be freely introduced into every cemetery, for the absorption of organic matters and of carbonic acid; and the most rapidly growing trees and shrubs should be selected, in preference to the slowly growing cypress and yew. The superficial space which should be allotted to each grave varies in different countries from 30 to 90 feet; the depth should be at least 6 feet. It is required by law that the grave spaces for persons above twelve years of age shall be at least 9 feet by 4, and those for children under twelve years, 6 feet by 3. It is likewise required that not less than 4 feet of earth should be placed over the coffin of an adult, and 3 feet above that of a child. The time which should elapse before a grave is disturbed for a new tenant varies with the soil and the distance of the body from the surface. Under favorable circumstances, a coffin containing an adult will disappear with its contents in about ten years; while in a clayey or peaty soil it will remain a century. It is generally assumed that a period of fourteen years is sufficient for the decay of an adult, but long before this time all will have disappeared but the skeleton. As a matter of expense, too, that of cremation is greater than burial at sea. In burial at sea the body would go at once to support other forms of life more rapidly than in the case of land burial, and without danger of evolution of hurtful products. See Burial; Cremation.
Diet. Although about seventy elementary substances are known to chemists, only a comparatively small number of these take part in the formation of man and other animals; and it is only this small number of constituents which are essential elements of our food. These elements are, in the order of their abundance, oxygen, carbon, hydrogen, nitrogen, calcium, phosphorus, chlorin, fluorin, sulphur, potassium, sodium, magnesia, and iron, with traces of silicon, lithium, and manganese.
Carbon, hydrogen, nitrogen, and oxygen are supplied to the system by the proteid group of alimentary principles (see Diet)—viz. albumen, fibrin, and casein, which occur both in the animal and vegetable kingdoms, and the gluten contained in vegetables. Animal flesh, eggs, milk, corn, and many other vegetable products contain one or more of these principles. The gelatinoid group also introduces the same elements into the system, when such substances as preparations of gelatin, calves' feet, etc., are taken as food. Carbon, hydrogen, and oxygen are abundantly introduced into the system of the carbohydrate group in the form of sugar or starch (which occur in
