It is best to introduce the oil into the pipes from outside the house, if possible, so that the odor which inevitably attends the process may be dissipated in the external air. The object being to ascertain the location of defects in the pipes inside the house, the examiner must feel certain, if he detects the odor of peppermint anywhere, that the vapor has come to him from inside the pipes, and not from the outside. If the ventilating-pipes are so constructed that the oil can not be poured in from the roof, then it must be poured into some basin or water-closet in the upper portion of the house. The peppermint should first be mingled with a pailful of hot water to promote rapid volatilization, and poured slowly down the pipe. After it is poured down, the openings at the upper extremities of the pipes should be closed, so that the pressure of the vapor inside the pipes may not be relieved in that direction. If the odor of peppermint, thus introduced with the precautions mentioned below, is perceived anywhere in the house, it is an indication that there is an opening in some pipe, through which sewer-air may escape. This opening may be a defect, or it may be due to siphoning of traps, or to faults of original construction. There will not usually be much difficulty in locating it with considerable exactness. _Special Precautions._ The peppermint should be kept on the roof, or on a window-sill outside the house, until needed, for it is so volatile that the vapor escapes through the cork, and if the odor gets into the house in this way, it will vitiate the examination. The person who pours the peppermint should remain on the roof or in the room where he does it, with the doors closed, until the examination is complete, for the odor will cling to his clothing and follow him wherever he goes for an hour or more. _Additional Remarks._ If bad odors have been noticed, and no defect can be found in the ways above mentioned, they may be due to decaying animal matter (dead rats, etc.), or (in the city) to defects in the plumbing of the adjoining house, offensive gases from which may penetrate the wall. The source of bad odors need not necessarily be in the immediate vicinity of the place where they are noticed, for the walls of buildings are full of channels and openings, through which offensive gases may be carried by currents of air, so as to emerge at a considerable distance from their origin. Thus, in winter, they are apt to be most noticeable near a fire. SUMMARY OF THE BEST METHODS OF DRAINAGE. For =houses= where there are =public sewers=: water-carriage. For =country houses=, if =isolated from sewers=, and where expense is no objection: water-carriage with subsoil drainage. In =villages= and =small towns, without sewers=: subsoil drainage (for slops), and pails (for excreta), frequently removed by proper officers.