carry the coal gases up the chimney. Cast-iron stoves, when red hot, may also allow, it is believed, this gas to pass into the room. A hot stove is also objectionable for the reason that small particles of organic matter in the air when falling on the stove become charred and yield unpleasant odors. These conditions may be avoided by nct allowing stoves to become too hot, by seeing that there are no cracks in the fire box, and by not completely closing the dampers. A gas stove or water heater should have a hood over it connected by a pipe with the chimney to carry off the products of combustion. With good ventilation, as by open windows, it may be possible to get along without this connection to the chimney, but care should be taken that no gas leaks from the feeding pipes, especially where rubber tubes are used, and that burners are free from soot, or otherwise the air of the room may be contaminated by carbon monoxide. This gas is less likely to be given off from oil stoves, as the perfect combustion of good oil does not produce this gas. An oil stove should not, however, be used in a tightly closed room. Hot-air furnaces. In this method of heating the air is drawn from the outside, through a pipe, over hot plates or tubes in the furnace, and conducted by ducts to different rooms of the building. Circulation of air in such a building is usually good, but the air is excessively dry from passing through the furnace, the water pans in these structures being entirely too small to supply the requisite amount of moisture. The futility of trying to supply the necessary . moisture by contrivances of this kind is evident when the quantity of water that should be evaporated for this purpose is considered. For example, Surgeon Clark of the United States Public Health Service cites the following: To supply a classroom of 35 pupils with 1,800 cubic feet of air each per hour at 70° F., with a relative humidity of 70 per cent for 7 hours, would require the evaporation of over 30 gallons of water, when outside air is taken at a temperature of 30° F., with a relative humidity of 70 per cent. Hot-water and steam pipes.-The system of heating buildings by circulating steam or hot water through pipes is efficient so far as the warming of all parts of the building to which the pipes lead is concerned, but is open to the same objection as furnace heat, inasmuch as the air is rendered very dry by their use. In some cases the radiator is placed under a window and an air duct leads to the outside of the building. The cold air becomes heated in entering the room by passing through the hot radiator. This plan is fairly efficient in mild weather, but when the temperature is low the air is frequently insufficiently heated, and persons sitting in the room are apt to close the air duct. Another objection is that the air in cold weather is usually dry, the relative humidity being sometimes 50 per cent or less, and passing through the radiator renders it still drier. In other 129054-193 cases hot water and steam pipes do not extend over the building, but the air is heated by passing over hot pipes in the basement. This method is little different from furnace heat and is no better than the latter unless moisture is added to the incoming air by means of steam jets or in some other way. Electric heating. This method of heating is very little used on account of the expense. It consists simply of resistance coils which heat the room by radiation and convection. Heating by this method has the same disadvantage as hot water and steam and requires special apparatus to provide moisture to the air. ` Water Supply. Good water is essential to life. It comprises about 70 per cent of the body weight and is necessary to provide elasticity and suppleness to the muscles, bones, cartilages, and tendons, to moisten various parts of the body so that they can perform their functions, and to act as a solvent for the food so that it may be absorbed. It also provides a fluid medium for the blood and lymph by which nutritive substances are taken to all parts of the body and waste products are removed. The quantity of water needed for each person for drinking and cooking is about 1 gallon per day; for washing and other purposes about 16 gallons per day. Many cities having large manufacturing plants supply a much greater quantity for each person; some as much as 250 gallons per day. Great care should be taken to prevent water that is to be used by human beings from being contaminated with the germs of disease; typhoid fever, diarrhea, dysentery, cholera, tuberculosis, and probably other diseases may be acquired in this way. The eggs of intestinal worms are sometimes present in water, and if this water is swallowed full size worms may develop in the body. These germs and parasites get into water through the discharges of infected human beings or animals, and in order to prevent well persons from becoming ill it is necessary that water should be kept free from human and animal filth or that steps be taken to remove it before the water is used. Water may be of good color, have a pleasant taste and no odor, and still be unfit to drink. Its quality can not be determined until the place from which it has been obtained has been inspected and an examination made to determine what substances it contains and if any disease germs or animal parasites are present. Water to supply cities is, for the most part, obtained from rivers and lakes, or from a reservoir made by throwing a dam across a small stream. If possible the drainage area from which the water is derived is in the hills or the mountains, where there are few, if any, habitations, for all surface water is contaminated by washings from the soil. Many privies are placed over streams or so near one that their contents are carried into it whenever there is a heavy rain. Stables and pigpens on the sidehills drain into the streams in the valleys. It is never safe to drink water from a stream; in thinly settled sections the danger may be small, but it should be remembered that if the discharges from one person suffering from typhoid fever are emptied, without previous disinfection, into a stream, or such discharges are washed from a privy or otherwise gain access to the stream, whoever drinks the water may contract the disease. This is well illustrated by the epidemic which occurred in 1885 in the town of Plymouth, Pa., with a population of about 8,000, at which time 1 of every 8 inhabitants contracted the disease. Rosenau states: Plymouth received its water from a mountain brook which drained an almost uninhabited watershed. The stream was damned at intervals, and the water was stored in a series of four small impounding reservoirs. The source of the infection was traced to a citizen who spent his Christmas holidays in Philadelphia and returned home in January. He contracted typhoid; the excreta were not disinfected, but were thrown either into the frozen creek or upon the banks within 25 or 30 feet of the edge of the stream. At this time the brook was frozen and remained so until spring. There came a thaw in March and the entire accumulation was washed into the brook and thence into the water main. Three weeks thereafter cases of typhoid by the score made their appearance throughout the town. On some days more than 100 new cases occurred. In all 1,004 cases were reported. Some estimates placed the number at 1,500-that is, 1 in every 5 of the inhabitants. There were 114 deaths. The epidemic was limited to the houses supplied with the town water or to persons who drank of the public water supply. The distinction was particularly emphasized on one street, where the houses on one side had one or more cases while the houses on the other side had none at all. The former were supplied by the town; the latter depended upon wells. This epidemic will ever stand out in the literature as a clear-cut instance of water-borne typhoid caused by the quick transfer of virulent material from a single case. It proves further that freezing alone was not sufficient to destroy the typhoid infection, and on account of the coldness of the water it is exceedingly unlikely that any multiplication of the typhoid bacilli occurred. The infection, although greatly diluted, was nevertheless sufficiently virulent to induce the disease in most of those who drank the water. It further teaches the lesson how one person is sufficient to defile the "pure waters of a mountain brook draining an almost uninhabited territory." This epidemic was the first large outbreak in America where the cause was definitely traced to the water supply. It stands out sharply in the sanitary annals of our country on account of the lessons it taught and the good influence it had in stimulating other cities to safeguard and improve their water supplies. Many cities obtain water from rivers which are foul with sewage. Such water has to be purified before it can be safely used. This is done by storing it in large settling basins, where much of the mud falls to the bottom, carrying with it many disease germs and other impurities; from these basins the water passes through sand filters, which are shallow reservoirs having at the bottom about 6 feet of filtering material. The top layer of this material is composed of about 3 feet of fine sand, which rests upon a layer of fine gravel, under which is a layer of coarser gravel covering a layer of broken stone. (Fig. 14.) The water flows from the filter through pipes which are placed in the bottom layer. While in the filter it is kept at a depth of about 3 feet above the sand. These filters if properly operated will remove over 99 per cent of the germs present in the water. The standard adopted by the Treasury Department for drinking water supplied to the public by common carriers in interstate commerce, which should be the standard for all drinking water, requires that there be not more than 100 germs in 1 cubic centimeter (15 drops), nor more than 1 colon bacillus in 6 teaspoonfuls of water. The colon bacillus is a germ found in large numbers in the intestinal tract of warm-blooded animals, and its presence in water may be considered valid evidence that the water has been polluted with intestinal discharges of man or some of the higher animals. From 1,000,000 to 5,000,000 gallons of water can be purified each day by the above-described filter if it is an acre in extent. Other filters, known as mechanical filters, if of the same size, can purify 100 times as much water in the time given. They consist of a tank containing a layer of sand through which the water passes after a small quantity (1 or 2 grains to the gallon) of alum or copperas has been added. These filters are useful where the water is very muddy, but they are more expensive to operate than the slow sand filters. Their action in removing germs is also not as uniformly high as the latter. Household filters are serviceable in rendering water free from mud, but no reliance should be placed upon them to remove germs. Bleaching powder, which is also called "chloride of lime" and "chlorinated lime," is ofter. employed to purify water. This action of bleaching powder depends upon the calcium hypochlorite which it contains. This substance combines with the carbonic acid in the water to form carbonated lime. The chlorine which is set free unites with the hydrogen of the water, and the oxygen thus liberated kills the germs in the water. A good bleaching powder will average FIG. 15.-A model well, cased with terra-cotta pipe, curbed 35 per cent of available chlorine. The quantity required to rid the water of germs varies from 1 to 3 parts of chlorine (3 to 9 parts of bleaching powder) to a million parts of water. This is a reliable, cheap, and efficient method of purifying water, except when it con |