“There are causes operating, as we all know, to destroy the sewage which, to a certain extent, will effect that end; but the question, as I understand it, is, whether those causes are really adequate to destroy the sewage, not partially but absolutely and entirely, during a given course of the river? _I do not think, in the present state of our knowledge, to pronounce an absolute opinion upon that point._ But if you ask whether it is wise to drink water into which you have put sewage, knowing that you have no means of getting that sewage out of it, that is a question which any one can answer for himself, assuming always the injurious character of sewage.” The fifth annual report of the Board of Health of Massachusetts (1875), contains the following, on the effects of oxidation, dilution, and deposition: “_Oxidation._--Although it is not practical, in the case of a running stream like the Merrimack, to trace the progress of the destruction of the organic material by oxidation, yet there is no doubt that a certain amount is so destroyed. The presence of nitrogen in the form of nitrites and nitrates is mainly due to the oxidation of nitrogenous organic material. In the last report of the Board, the reasons are given which lead to the belief that the effects of oxidation have been overrated, although they are not, on the other hand, to be depreciated. “_Deposition._--Much waste material, thrown into rivers, is made up wholly or in part of substances insoluble in water. A portion, and a very considerable portion, even in a running stream is deposited upon the bottom or stranded upon the banks. At the time of spring freshets much that during the summer may have been deposited at one part of the stream, in the bed or on the banks, is washed up again, and mingling with the earthy materials, held in suspension, is swept onward to the sea or enveloped in the earthy matter, especially if this be of a clayey nature, is deposited lower down the stream. These spring freshets are relied upon for cleansing banks used for infiltration. “_Dilution._--By far the most important reason of the apparent disappearance of sewage and other waste material, is the fact that the amount of solid matter is so small compared with the volume of water into which it is thrown, that it is disseminated through the mass and thus lost to observation, and in many cases to chemical test.