tially, aerobic in its action; whether, that is to say, the suspended impurities are attacked therein by a mob or by a disciplined army of organisms, a question of great practical importance in correlating the dimensions of biolytic beds with the work to be done in them. Be this as it may, the effluent from the bacteria bed is practically free from any organic matter in suspension, while the filtrate subsequently derived from the coke beds issues minus some 99 per cent. of its original impurities. This filtrate is a clear, odourless fluid, which keeps unchanged in closed or open vessels for any length of time, satisfies the demands of the Thames Conservancy, and has even been drunk by bold men without ill-effects following. Mr. Chambers Smith's report,2 already quoted, states that previously to the introduction of the present system of sewage treatment, Sutton spent 1,2501. per annum on chemicals, sludgepressing, and farm operations, without producing a satisfactory effluent; but when, as the urban council intend, the bacterial plant has been extended sufficiently, to deal with the whole, instead of half the sewage of the town, the annual cost of working will not exceed 700l. Meanwhile the farm will be available, for sale, or use as a recreation ground, little more than an acre of space being required for filter beds capable of dealing with 400,000 gallons of sewage in every twenty-four hours. Mr. Cameron, the city surveyor of Exeter, is a third investigator whose "septic" system of sewage purification was adopted by his own council in 1896 for the treatment of the sewage derived from St. Leonards, a suburb of the city, having a population of 1,500 souls, and a flow of sewage averaging 54,000 gallons per twenty-four hours, each gallon containing 241 grains of suspended matter- a weak compound, it may be remarked, in comparison with that of Sutton. Crude sewage, in this case, is allowed to run direct from the drains into the "septic tank," A (fig. 3), a chamber hermetically closed to light and air, and of sufficient capacity for the reception of one day's flow. Such gravel and sand as accompany the sewage are arrested in the catch-pit, B, and the liquid then passes, very slowly, to the outlet, c, its contained impurities thus resting for twenty-four hours in the chamber. There it is attacked by organisms of the anaerobic type, for whose operations the airless space is designed, and who can be watched at their work from the tower, D, occupying the centre of the tank and accessible by the manhole, E. From 1 Dibdin, Purification of Sewage, p. 65. 2 Report of Surveyor to Surrey Urban Council, February 1898. the windows with which the watch-tower is furnished, a leathery scum is observed to float on the surface of the contained fluid, while the floor is covered with a deposit of heavier matter. Both the scum and deposit are densely peopled with microorganisms, which bring about a constant transference of particles from the upper to the lower layer, and vice versa, in the following way: As the organic substances in the scum become decomposed under the anaerobic attack, their débris, or ash, drags here and there a particle to the bottom where other microbes fall upon it, and by further rearrangements of its molecules give rise to bubbles of gas which buoy it back to the surface. There the bubbles burst, the particle once more falling, but only to be lifted again and again in the same manner until it is quite decomposed. The septic chamber is alive with these rising and falling particles which, in the course of their endless journeys, bring the liquefying anaerobes into contact with all the suspended matter diffused throughout the tank, gas meanwhile accumulating in the roof, whence, not being itself an illuminant, it is carried to Welsbach burners that light the works. During the first year's experience of the Exeter "septic tank," the scum varied in thickness from 4 inches in winter to 1 inch in summer, while the heavy deposit amounted in the same period to some 5 tons, representing a loss of 20 grains out of 24 grains of the suspended matter originally contained in the raw sewage.1 Practically no sludge is produced, such substances as paper, rags, and even feathers disappearing in the chamber; while the heavy deposit is found, on examination, to consist of an insoluble residue, or asb. derived from the decomposition of organic matter, mixed with a large proportion of mineral matter too finely divided for arrestation by the catch-pit. The effluent from the "septic tank," having its suspended matter thus thrown into solution, is suitable for land treatment, but is disposed of at Exeter upon nitrifying aerobic 1 Cameron's Report: Leeds Congress of the Sanitary Institute, 1897. filters, similar to those employed at Sutton and already described. Five of these are provided, so that while four are being alternately and intermittently charged a fifth rests. Filling and emptying are accomplished automatically by means of a device, the invention of Mr. Cameron, which reduces the amount of manual labour required for the management of the plant to a mere trifle. The nitrifying filters occupy a space of 400 square yards, while the septic chamber itself has an area of 130 square yards, making together, 530 square yards, or say one-ninth of an acre. Upon this small space, with a minimum of labour, without the use of chemicals, the production of sludge, or the creation of any nuisance, the excreta of 1,500 people are dealt with by Nature's scavengers, while the filtrate which ultimately reaches the Exe has, like that at Sutton, been drunk by bold men with impunity. Although many towns, other than Sutton and Exeter, which were recently nicknamed the Mecca and Medina of the sanitary engineer, have already adopted, or are about to adopt the Bacterial Treatment of Sewage, the time has not yet arrived for expressing an opinion on any of the plans described, or for an economic presentment of the case for biolysis. Some figures, which are not estimates, have, by the kindness of Mr. Chambers Smith, been quoted, but it must be remembered that a good deal of pioneer work was done and expense incurred at Sutton which will be saved in future installations on the same principle. It has been questioned whether the biolytic treatment of sewage might not add to such dangers as communities already run from pathogenic germs, whose multiplication may presumably be encouraged in bacteria beds and filters. Not everything is at present known as to the ways of the wily microbe, but already the biologist is prepared to give him good testimonials in this regard. "The putrefactive germs," says Dr. Sims Woodhead, "have nothing to do with the production of disease under natural conditions; in fact, the addition of large quantities of such germs is said to interfere with the action of, or even entirely destroy, many disease-producing germs." This gentleman's experiments at Exeter further demonstrate "that crude sewages containing about half a million organisms per cubic centimetre, when inoculated into the filtered effluent of a septic tank, developed more than a thousand millions in five days, thus overwhelming any pathogenic germs that might be present.' Dr. Rideal's paper, Sanitary Institute, Birmingham, 1899. T Dr. Pickard specially investigated the typhoid microbe with reference to the action upon it--first, of crude sewage, second, of the septic tank, and third, of the coke filter; finding that sewage" is not only a bad food, but an actual poison" to this bacterion; that in the septic tank it suffered rapid destruction; and that the filter beds effect a further biological elimination; "so that there is no chance whatever of the filtrate causing typhoid fever if passed into the river." Dr. Rideal, a third authority, takes the same view, remarking in the paper already referred to: "It is well known that the pathogenic bacteria do not, fortunately, thrive much below blood heat, and that they are rapidly crowded out and destroyed by the ordinary bacteria existing in common waters, and still more so by the immense numbers existing in sewage." These conclusions are confirmed by the bacteriological results obtained in the experiments made at Lawrence, where special attention was paid by skilled biologists to the point in question, which there, as here, was resolved in favour of the microbe. A further problem has yet to be considered-that, namely, of the suitability of the bacterial treatment for the sewage of manufacturing towns, where the drains are charged with various matters presumably poisonous for either aerobes or anaerobes. Experiments on this point are being carried on, notably at Manchester, Bradford, and Leeds; while a "septic" installation at Yeovil, which deals with 200,000 gallons a day, is said to have operated successfully since 1896 on a strong sewage rendered especially difficult to deal with on account of the presence therein, in large quantities, of leather-dressing products. While, however, economics, pathogenic fears, and manufacturing refuse remain, so far as sewage is concerned, "on the knees of the gods," agriculturists will be interested in the glimpse which Mr. Scott-Moncrieff vouchsafes them of a nitrateproducing region, less remote than South America and more accessible, it may be hoped, than Professor Crookes' nitrogenstore. Meanwhile, there remain the isolated homes of country gentlemen and farmers, for whom the biolysis of sewage offers a tried, cheap, and complete issue out of afflictions which, in some cases, and on some soils, are serious enough. A pit full of stones and a coke filter are all the apparatus required to permit the drainage of a great country house being harmlessly thrown into a stream, or a piece of ornamental water; or, if Scott-Moncrieff's nitrifying chamber be adopted, utilised with advantage in the greenhouse and conservatory. Mr. Dibdin, Mr. Scott-Moncrieff, Mr. Cameron, and Dr. Vivian Poore, each occupying a camp of his own, represent the practical champions of the Bacterial Treatment of Sewage; and if no mention has been hitherto made of the last gentleman, that is because his "dry" method of dealing with excreta has been already declared outside the scope of this article, which, for reasons adduced, deals with water-borne sewage only. No loss to the reader will thus accrue, since Dr. Poore has set forth his own case so often, so well, and, in his little book entitled "The Dwelling-house," so charmingly, that the writer's silence may well be forgiven. But apart from these practical pioneers, a number of distinguished bacteriologists and chemists have paid, and are increasingly paying, great attention to the various problemsnone of which are yet completely thrashed out-that arise in connection with the subject of this review. Among them, Drs. Sims Woodhead, Rideal, Kenwood, Butler, and Houston, together with Messrs. Kaye Parry, Adeney, Pearmain and Moore are conspicuous, and it is a matter of regret that their brilliant work cannot be formulated in terms sufficiently untechnical for employment in a popular exposition such as this essay. It must suffice to say that, while differing upon matters of detail, these scientists all agree that future plans for the disposal of sewage must consist, first, in artificially hastening the natural process of putrefaction, and afterwards in oxidising, for the purpose of rendering inoffensive, and possibly valuable, the products of such putrefaction-the functions respectively of Pasteur's anaerobes and aerobes. The Long House, Leatherhead. DAN. PIDGEON. FLOWER AND FRUIT FARMING IN IV. FRUIT GROWING UNDER GLASS. RAPID EXPANSION OF THE HOT-HOUSE INDUSTRY. No other industry connected with land has shown such great expansion in this country during the last thirty years, and especially during the last twenty, as the cultivation of fruit and |