anxieties, the often permanent darkening of life, the straitened means of subsistence, the very frequent destitution and pauperism, which attend or follow such suffering, death statistics, to which alone I can refer, testify only in sample or by suggestion."
The means by which infection is likely to be conveyed to households are far too numerous to be dealt with in a single lecture, and I have thought it best to select for consideration three or four of what I feel to be among the more important, and to deal with these in detail.
In a report on an epidemic of enteric fever at Croydon, in 1875, Dr. Buchanan, F. R. S., makes use of the following words: "The air of the sewers is, as it were, 'laid on' to houses." That significant expression "laid on" comes in aptly, as giving prominence to the special features of one of the channels for conveying infection to households, to which I propose drawing your attention. From the inside of every ordinary dwelling-house there pass certain waste-pipes intended to convey liquid refuse, first to the house-drains without, and thence to the public sewers. It is the custom to regard these conduits as passing from house to sewer, but this evening I would ask you to compare them with the pipes for the supply of coal-gas, and to view them rather as passing from the sewer as a center to the periphery within our dwelling-houses. In our comparison the public sewer may be regarded as corresponding with the gasometer; the house-drain and the waste-pipes as representing the service-pipes for gas; and the so-called "trap" indoors as taking the place of the metal tap found in connection with each gas-bracket. Sewer-air, even in its normal state, is a grave source of danger to health; but when the sewers receive in their course along the streets the infectious refuse discharged from houses where specific disease prevails, then the sewer-air harmful hitherto is changed into an intense poison.
How is it usually sought to debar this poisonous agent from dwellings? The sole means adopted, in nine cases out of ten, consists in placing at some point of the pipe which connects the interior of the house with the interior of the sewer a small body of water which is known as a "trap," and which is designed to act as a barrier to the passage of all sewer-air. The contrivance most commonly resorted to is the so-called bell-trap, an apparatus in which the rim of a bell-shaped cup is suspended in a small body of water contained within a circular depression. This form of trap is of all the least efficient; it is not only one in which the water-lock constituting the trapping may at any moment be entirely removed at the will of the individual, but at its best it provides between the house and the sewer a layer of water only about one half or three quarters of an inch in depth. Even the most efficient of all traps, the so-called "siphon-bend," is not much better. Dr. Andrew Fergus maintains that trapping has but little effect in keeping sewer-air out of houses, as the entrance of the con-
