For main divisions of all methods of sewage treatment two factors seem to be of primary importance, viz. the agencies which bring about this purification, and the way in which these agencies are employed. Now, it will not be denied that all agencies are natural ones, whether the process employed is a purely chemical one, a purely “bacterial” one, land treatment pure and simple, or a combination of these, and, at the present time no such thing as an artificial agency is known; indeed, it is perhaps not too much to say that there cannot be such a thing as an artificial agency. Hence it is impossible to divide sewage purification methods in this respect by the agencies employed, and one is bound to fall back upon the way in which these agencies are employed. Here it is no longer open to argument whether a chemical process or the contact bed system—oxidation bed system—is artificial, or whether the land treatment is natural! For who would deny that masonry or concrete tanks and the materials contained in the same are artificial products—i.e. products formed by man—and that land is a natural product—i.e. formed by nature—and that further the soil is the natural home of bacteria. Hence it must be perfectly clear, even to a casual observer, that the line of demarcation drawn by the Commissioners between all known systems of sewage purification is a correct and legitimate one, and that all objections to such a division are based on misconceptions. Concerning land treatment, the Commissioners observe, “We doubt if any land is entirely useless,” but further on they observe that peat and stiff clay lands are generally unsuitable for the purification of sewage. Concerning peat, nobody acquainted with the subject would probably differ from their conclusions owing to the great amount of moisture contained in this material; but as to clay soils, the Commissioners when making this statement must have known that there are several successful sewage farms on this kind of land in existence, such as the sewage farms at South Norwood, Wimbledon, Warwick and Leicester, not to mention others. In the case of Leicester, although the land is a very dense boulder clay, the Corporation of this town have just purchased the freehold of the farm for about 160,000_l._ Dealing with the artificial processes from a chemical point of view, the Commissioners are of opinion that it is practicable to produce by these processes alone, either from sewage or from certain mixtures of sewage and trade refuse, effluents which might be discharged without fear of creating a nuisance, and that in consequence the Local Government Board would be justified in modifying, under proper safeguards, the present rule as regards the application of sewage to land. The artificial processes referred to in the observations appear to be the following:—