The results of all sanitary investigation indicate clearly the vital necessity for the complete and speedy removal from human habitations of all matters which, by their decomposition, may tend to the production of disease, and early measures should be taken by the authorities of all towns, especially those which are at all compactly built, to secure this removal. The means by which this is to be effected are to be found in such a combination of water-supply and sewerage, as will furnish a constant and copious supply of water to dissolve or hold in suspension the whole of the waste matters, and will provide a channel through which they may be carried away from the vicinity of residences. If means for the application of the sewage water to agricultural lands can be provided, a part if not the whole of the cost of the works will be thus returned. Concerning the details of house drainage, it would be impossible to say much within the limits of this book. The construction of water-closets, soil-pipes, sinks, etc., are too will be understood to need a special description here. The principal point, (aside from the use of pipes instead of brick-sewers and brick house-drains,) is what is called in London the system of Back Drainage, where only principal main lines of sewers are laid under the streets, all collecting sewers passing through the centres of the blocks in the rear of the houses. Pipes for water supply are disposed in the same manner, as it is chiefly at the rears of houses that water is required, and that drainage is most necessary; and this adjustment saves the cost, the annoyance and the loss of fall, which accompany the use of pipes running under the entire length of each house. Much tearing up of pavements, expensive ditching in hard road-ways, and interference with traffic is avoided, while very much less ditching and piping is necessary, and repairs are made with very little annoyance to the occupants of houses. The accompanying diagrams, (Figs. 48-49,) illustrate the difference between the old system of drainage with brick sewers under the streets, and brick drains under the houses, and pipe sewers under main streets and through the back yards of premises. A measurement of these two methods will show that the lengths of the drains in the new system, are to those of the old, as 1 to 2-1/4;—the fall of the house drains, (these having much less length,) would be 10 times more in the one case than in the other;—the main sewers would have twice the fall, their area would be only 1/30], and their cubic contents only 1/73. [Fig. 48 - OLD STYLE HOUSE DRAINAGE AND SEWERAGE.] Fig. 48 - OLD STYLE HOUSE DRAINAGE AND SEWERAGE.