The modern house drains into a sewer, which is necessarily always foul and filled with the gases of putrefaction. These gases are the result of microbial action. The sewage water is full of microbes, the gases of putrefaction are the gaseous 'toxins' (CO₂, H₂S, CH₄, NH₃, &c.) which result from their growth. The air of the sewer is necessarily harmful in itself, and the presence or absence of microbes in the sewer air is a matter of practically small importance. The house drains are necessarily foul as well as the sewers. We hear a great deal about 'self-cleansing' sewers, which shows how ignorant are the surveyors and others who use such terms. A glazed pipe, with a good gradient, may be less foul than a rough sewer with insufficient gradient, but you can no more have a 'self-cleansing' sewer than you can have a self-cleansing saucepan or chamber-vessel. The foulest place in a house is the kitchen sink, with its vegetable and animal _débris_, such as cabbage-water, grease, &c. Sanitary engineers are trying to cleanse these places by automatic flushing with cold water, which, to say the least, is enterprising. A few years ago 'fat traps' were fashionable, but were soon found to be intolerable from their inexpressible foulness. It must be remembered that wherever along a line of drainage you get stagnation there must be putrefaction, and it must be borne in mind that every 'trap' which is a contrivance for ensuring stagnation is necessarily a place where putrefaction is liable to take place. Traps may keep back the smell of the street sewer in house pipes, but it must never be forgotten that they are undesirable evils in themselves. The efforts of modern sanitary engineers are directed towards ensuring that the gases which inevitably result from putrefaction in sewers and house-drains should be as much as possible diluted with external air before we breathe them. The sewer gratings in the streets give off foul gases at the pavement level, especially in the summer. The ventilating pipes give off foul gases at the roof level, close to the water cisterns. The traps beneath every W.C. and sink are all spots where putrefaction may and often does take place. The gullies in the front and back areas of the house are also liable to be foul. Here I would insist that every gully on the ground level should, when possible, be freely exposed to the air, so that the wind may blow over it. This, in London, is impossible, as these gullies are necessarily surrounded by the walls of the area, and in still, muggy weather these areas must contain a large amount of gaseous toxins. I insist upon this point because I see the town architect making the mistake in the country of enclosing the kitchen and pantry gullies by walls (to form a kitchen yard), so that any emanations which arise from them are liable to be drawn into the house through the open windows. Such an arrangement ought, when possible, to be carefully avoided.