daily results have been obtained on this basis from each of 26 water purification plants in operation in that country. There seems to be no good reason why the bacterial results to be obtained from the various water purification plants now in operation and about to be built in this country should not be comparable with those obtained abroad. This is especially true in view of the growing appreciation of the fact that the residual numbers of bacteria in a filtered water should receive attention as well as the percentage of bacterial removal. Taking everything into consideration, it would appear to your Committee to be advisable to adopt forty-eight hours as a standard period of cultivation under the conditions noted above. Before making a final recommendation there is requested a further expression of opinion on the part of the members of the Section of Bacteriology and Chemistry."

CHAPTER V.

THE REMOVAL AND DISPOSAL OF SEWAGE.

THE term sewage includes not only human excreta, solid and liquid, but also the waste water and impurities coming from human habitations. The term sewage, however, does not include such impurities as proceed from manufactories, such as the refuse from dye-works, gas-works, etc.; these are termed manufacturing impurities. From a hygienic standpoint the human excreta are the most important constituents of sewage. The sewage of towns usually contains, besides human excreta and household wastes, the water used for washing and sprinkling streets, as well as the rain that falls which is not stored for household use. The total quantity of sewage depends largely upon the amount of pure water supplied per head per day. Sewage has an average composition of 998 parts of water, I part of urine, and 1 part of organic matter.

The Removal of Sewage.-The removal of sewage from the dwelling is accomplished by several different methods. That in general use in towns is by means of water. This system necessitates the introduction of the necessary waste pipes for the removal of the sewage itself, the introduction of a supply of water sufficient to flush out the drain pipes and keep them free from sewage. It also necessitates arrangements for the disposal of the

sewage.

Water-closets.-Where water is employed for the removal of sewage the water-closet forms a most important factor in the system. The qualities required by all the appliances of a water-closet are durability, simplicity, accessibility, cleanliness, and general effectiveness. The

The

old-style pan closet (Fig. 30) is no longer in use. principal forms of closet that are now in use are the

a

FIG. 30.-Pan closet.

hopper (Fig. 31), some form of wash-out or wash-down closet for private dwellings (Figs. 32, 33), and the

FIG. 31-Hopper closet.

FIG. 32.-Wash-out closet.

trough closet or latrine for schools and public institutions.

The supply of water for the wash-down closet is obtained by the introduction of a separate cistern, used exclusively for the water-closet, generally termed a "water-waste

FIG. 33.-Wash-down closet.

preventer" (Fig. 34), because only a limited supply of water is available for delivery. The amount of water usually supplied in the cistern is about 15 liters.

The

FIG. 34-Water-waste preventer.

cistern is placed at some height (not less than a meter) above the closet, and has an exit pipe of considerable size, so that the water may descend with sufficient force to flush effectually the closet.

The position of the closet chamber is of importance. It should always be arranged along the outer wall of a building, so as to afford ventilation into the open air, and not into an air shaft. The closet itself should be along the inner wall, opposite a window, so as to afford plenty of light to detect any defects.

The arrangement of a bath-room, in which all the

N

FIG. 36.-S-trap.

FIG. 37.-Bell-trap.

FIG. 38-Anti-D trap.

modern improvements in the sanitary removal of sewage are supplied, is shown in Fig. 35. In the modern dwellings now being constructed the conveniences supplied in bath-rooms are important factors in conserving the health of the individual as well as of the community.

Traps. A trap is a bend in the pipe which is filled with water so as to prevent the entrance of sewer or drain air into the house. It consists of a water seal in the pipe.