4. _The Sewers and Drains.--How to Keep out Sewer Air_.--The most perfectly flushed sewers that are made, under the latest and fullest sanitary light, must, owing to the constant entrance of greasy and other adhesive material, contain more or less of particles that "stick," and also more or less of fungi and mold; so that here, shut away from light and air, goes on the peculiar fermentation that fits it for the soil or habitat of the malarial germ. These germs, the soil once ready, take possession and multiply, whether that soil be a sewer or the blood of a person who sits calmly unconscious in a gorgeous chamber above, with a small continuation of the sewer extending untrapped up to his washbowl.-- DR. DERBY. Keep constant watch of your traps and drains. Cultivate the faculty of detecting sewer gas in the house. Always fear a smell; trace it to its source and provide a remedy. At the same time, bear in mind that it is not always the foul smell that is most dangerous. There is a close, sweet odor often present in bathrooms, and about drains, that is deadly as the Upas tree. Bad air from neglected drains causes not only fevers, dysentery, and diphtheria, but asthma and other chronic disorders. Illuminating gas, escaping from pipes and prevented from exuding by frozen earth, has been known to pass sidewise for some distance into houses. Thus also the air from cesspools and porous or broken drains finds its way, when an examination of the household entrance to the drain fails to reveal the cause of an existing effluvia. But, however bad the drain may be outside the house, there is little to fear provided the gas can escape externally. Every main drain should have a ventilating pipe carried from it directly outside the house to the top of the highest chimney. The soil pipe inside the house should be carried up through the roof and be open at the top. Digging for drains or other purposes should not be allowed when the mercury stands above 60°; but if, as in repairs of pipes, it becomes necessary to dig about the house in hot weather, let it be done in the middle of the day, and replace the turf as speedily as possible. If the soil be damp, or the district malarious, sprinkle quicklime upon the earth as fast as it is turned. _How to Clear Waste Pipes_.--The "sewer gas," about which so much has been written, and which is so justly dreaded, is not, as many suppose, the exclusive product of the sewer. Indeed, the foul and dangerous gases are not only found in the sewers themselves, but in the unventilated waste pipes, and those which are in process of being clogged by the foul matter passing through them. Any obstruction in the soil or waste pipes is therefore doubly dangerous, because it may produce an inflow of foul gas into the pipe, even though the entrance to the sewer itself has been entirely cut off.