Thus it is that to-day the problem of sewage disposal, while arousing general interest, is recognized as one which requires more than the common sense of an average person, that the force and principles involved are understood to be not those in common use, and that, for successful disposal of sewage, special knowledge and judgment are required. Whatever the character of the sewage and whatever the kind of soil available for treatment, the method of dealing with sewage most obvious to most people has been to discharge the sewage directly into the nearest watercourse. This has been the practice of cities as well as of individual houses in the past, and the practice is very difficult to check because of the economy of this method of disposal. In many cases there is no objection to this method, and where a large stream is available, where no use is made further downstream of the waters for drinking purposes, and where the volume of water in the stream is sufficient to dilute the sewage to a point where no odors or objectionable appearances result, it would seem most uneconomical to adopt any more complicated method of disposal than by simply carrying the outfall pipe into the main bed of the stream. In New York State, and in a number of other States, the number of which is continually increasing, such direct discharge, however, is not permitted by law except under certain conditions. In New York State it is required that any house, butter or cheese factory, manufacturing establishment, or village shall obtain the permission of the State Commissioner of Health before such a method of discharge be adopted, and in order to obtain this permission it must be definitely shown that the conditions of the stream are such that no reasonable objection to this method could be urged. The policy of the various Departments of Health in the United States is gradually becoming more and more rigorous in the matter of prohibiting the discharge of crude sewage into watercourses, and it is wise to make very sure that the discharge of sewage into streams is above the suspicion of a nuisance before adopting this as a suitable method. Rather would it seem better to provide for some method of treatment and allow only purified sewage to go into the stream than to run the risk of being forced in a few years to reconstruct the entire line of outfall pipe, with perhaps an entire reconstruction of the plumbing within the house. The problem of treatment is the question of so modifying the character of a large volume of dirty water that it shall neither injure the quality of any drinking-water into which it may be discharged, nor cause objectionable odors, nor present disagreeable appearances in any body of water into which it may be emptied.