In addition to the above disadvantages associated with discharging storm water into sewers, the sewage owing to its increased bulk is more difficult of disposal, whatever method of disposal be adopted. The size of the sewers and of storm-outfalls into the nearest river or the sea must be regulated so that they are equal to these sudden strains on them; or the =Separate system=, by which the rain is carried in special conducts to the nearest river, must, in the alternative be adopted. The objections to this plan are that it necessitates a double system of sewerage, and does not allow of the useful scouring effect of rain on sewers. Where it is feasible, and particularly in small country towns, its adoption is advisable. In such cases the old brick drains are used for carrying off rain-water, while new _pipe-sewers_ are employed for carrying the sewage. Such pipe sewers are not liable to become fouled, and on account of the decreased dilution of the sewage can be made smaller than brick-sewers. Sewers being closed conduits containing sewage, it is highly desirable that the gases resulting from decomposition should be freely diluted. Such gases in unventilated sewers may find their way through intercepting traps into the house drain. The danger from this source has been considerably exaggerated. =Ventilation of the sewer= is, however, desirable. This has been commonly accomplished by gratings opening at intervals directly into the middle of streets. In narrow streets, the stench from street-grids is occasionally a source of complaint, and may cause malaise and ill-health. Charcoal traps placed below sewer grids to intercept offensive gases have been found to be of little use. The best plan is to do away entirely with surface ventilators, and carry up iron shafts or brick shafts lined with stoneware pipes above the level of all neighbouring houses. The only difficulty in adopting this plan is the difficulty in securing premises to erect such shafts up houses, although no danger attaches to the practice.