The first step is to ascertain whether there is a trap outside the house disconnecting the sewer from the house system and permitting inspection. If there is not, the first thing to be done is to make an excavation and open the drain at the proper point for placing such a trap. The next step is to set the water flowing in the various closets and watch the flow at the external trap, or opening, which has been made to ascertain whether there is any obstruction in the pipe within the house. If the sewer is properly arranged for inspection, as has been above suggested, to determine whether there is any leakage from the sewer under the house will be an easy matter; if, however, it is buried beneath the cellar floor, as is usually the case, an excavation should be made along the floor in the line of the pipe, with a view to having it properly arranged, as well as for the purpose of examining the soil. It may also be tested by opening the upright soil-pipes at the farther end of the house-drain at the height of three or four feet above the floor and pouring water into it, having temporarily stopped up the drain at the external trap or opening. If the water remain at a constant level in the upright piece, the sewer is water-tight; if not, the leakage may be ascertained by the rate at which it sinks. Having settled this, the next point is to determine whether all the soil-pipes are air-tight and properly trapped. The test usually applied for this purpose is the pouring of a small quantity of strong oil of peppermint, followed by a dash of hot water, into the top of the soil-pipe, which should always pass through the roof and be freely opened to the outer air. If the odor of the oil is perceptible in the house, it indicates a leak, which must be further sought for. Ether may be used for the same purpose. The smoke test is, however, the best, but it requires a special apparatus which as yet is little used in this country. It is applied by a small machine with a fan, by which the smoke from burning cotton-waste saturated with oil, or of coarse brown paper impregnated with sulphur, can be blown into the pipes; this locates leaks with great precision. It is not, of course, expected that a physician will personally make the examination necessary to determine whether the plumbing of a house is in good order, but he should be able to make it, if necessary, if for no other purpose than to know whether the inspector employed for the purpose understands his business.