I have sketched above, in a very hurried manner, the main outline of a system of house-drainage which may be accepted or which may be recommended by a physician with confidence of securing a good result. To go more into detail in technical matters would be out of place in a paper of this character. Before leaving this subject, however, it is important to call attention to the fact that what is recognized in our houses as sewer gas is in far greater degree the product of decomposition taking place within the house-drains themselves than the product {224} of decomposition in the distant sewer forced into the house through its connecting drain. It is emphatically a case of the beam in our own eye as compared with the mote in the eye of our neighbor. It is a rule which has exceptions, but they are few, that the contained air of the house-pipes is far worse than the contained air of the sewer; and the conviction is growing that the use of a trap to the main drain between the house and the public sewer is more often objectionable than advantageous. Such a trap always tends to check the flow of the drain and to induce deposits whose decomposition is objectionable. Wherever the abandonment of the trap is anything like universal the considerable ventilation of the sewer thereby secured brings its atmosphere to a condition which makes it not objectionable, and generally useful, as a source of movement in the air of the interior drain- and soil-pipe. (_a_) Public sewers are more or less good or bad entirely according to their character and condition. As a rule, a well-flushed sewer which is used for no other purpose than the removal of foul waste, built on what is called the separate system, and automatically flushed at least daily, may be considered to be, if well laid and tightly jointed, absolutely safe. A public sewer of large size and of irregular construction, receiving not only household wastes, but the wash of streets as well, may be regarded at least as an object of grave suspicion. These general statements may be so far qualified by the character of the sewers of each class as to run very nearly together; that is to say, separate sewers, with leaky joints, irregular grades, defective alignment, insufficient flushing, and inadequate restriction as to the matters they are to receive, will be an intolerable and dangerous nuisance; on the other hand, a large brick sewer built in the best manner and of the best material, with sufficient fall and sufficient supply to maintain itself in a cleanly condition, is free from the serious drawbacks which usually attach to sewers of this class.