But the late Lord Bramwell’s Royal Commission on Metropolitan Sewage Discharge established two very important points of general application, namely:— 1. The principle of separation in works of sewerage and drainage; and 2. The fact that the suspended matters in town sewage can be very effectually removed from its liquid by _simple deposition_ without the aid of any chemical reagent. [Sidenote: 1887. The chemist Dibdin discards chemical reagents in favour of M. Pasteur’s aerobic organisms.] And Mr. Dibdin three years later began to demonstrate the mistaken policy of adding lime or any other precipitating agent in any quantity likely to arrest the natural agency of abundant bacterial life, which ultimately disposes of all dead and effete organic matter by forming gases or natural compounds, with more or less offence to human senses, according to the supply of oxygen and rate at which these bacteria can carry out their work. [Sidenote: Leeds and Exeter.] It was soon found that the bacteria of two classes, aerobe and anaerobe, abound in sewage, and the latest Leeds experiment with the continuous or trickling filter show the marvellous rapidity with which the _aerobic_ microbes at any rate, can accomplish their task where air and liquid sewage are sufficiently diffused in the pores of a filter; while Mr. Cameron, C.E., at Exeter has shown rapid evolution of gases and considerable solution of organic solids by _anaerobic_ microbes in a septic tank. But the enthusiasm of inventors and their converts has made too much of the benefit to the human race supposed to be conferred by the bacterial discovery of M. Pasteur as applied by them to sewage treatment. Without detracting from the credit due to the great French savant and other bacteriologists who have followed up his interesting studies of ferments for the last fifteen years, the practical man may well ask how much forwarder have we got in the main and pressing business of purifying our rivers—as a consequence of clearer knowledge of minute forms of life? [Sidenote: Intermittent filtration.] The late civil engineer Bailey-Denton demonstrated, thirty years ago at Merthyr Tydvil, the best conditions of intermittent downward filtration, and his filters there and at Kendal, Abingdon, etc., are still doing their work efficiently to this day, while the coke, coal, clinker, burnt ballast, etc., beds, so popular of late, are clogging up after a few years of more careful treatment than was ever accorded to an acre of land under sewage. Anaerobic action has also been proceeding in the old sewers of most towns and, as it has now been proved that there is no advantage in the exclusion of air, upon which Mr. Cameron laid so much stress when he brought his Exeter tank to public notice in 1897, there can be no novelty except its name attaching to the anaerobic or _septic_ system, which has thrown many sanitary authorities off their balance of late years.