he had no doubt but that the subject, in the course of a few years, would be discussed in a way that at present was not possible. The knowledge of the habits and methods of the organisms which carried on the work of putrefaction and purification, outside of the laboratory, was at present of a most meagre kind, the attention of bacteriologists having been almost exclusively devoted to the study of organisms in relation to disease. Referring to the diagrams, he said, that in the case of Col. Waring's upward “strainer no doubt a considerable breaking up of the organic matter occurred, but it was a mistake to suppose that any large provision of air was required for this most important part of the general process. There were reasons for believing that the work of liquefaction was carried on first by aerobic organisms which so completely exhaust the oxygen contained in sewage that it becomes possible for anaerobic organisms, which are equally active, to finish the process. Their combined operations would besides other products yield a large amount of free ammonia, the presence of which in the effluent is always a proof of the activity of the organisms. Again, referring to the diagrams he said, that the downward filters of Col. Waring and Mr. Lowcock with special provision for mechanical aeration would probably be found to be applicable to the final mineralisation of the organic matter by the special organisms of nitrification. Certainly such appliances as had been described did not represent anything approaching to the full process of conversion from the organic to the inorganic state. For instance, any apparatus which provided for the deposition and removal of the organic sludge previous to the bacteriological treatment of sewage, as shown in Mr. Lowcock's diagram, was obviously defective inasmuch as it deprived the organisms of the food which it was their function to liquefy and mineralise, completing the cycle of nature from the effete products of animals to the nourishment of growing plants. He had no doubt that this process to which he had given the name of "biolysis," would before long be looked upon, on its practical side, as a most important branch of the science of Bacteriology.

Dr. S. RIDEAL (London) said although the experiments of Col. Waring were new to him, yet they confirmed the results of those already published by the Massachusetts Board of Health, and by Mr. Dibdin, of the London County Council, whose work, judging by the report issued by the Main Drainage Committee in the summer, seemed to be very far ahead of the Massachusetts experiments. The terms "filter" and "filtration," as applied to these methods for purifying sewage are not happy ones, as these terms are now better restricted, as Dr. Down has himself pointed out, to the removal of bacteria as well as of suspended matter from liquids; and he thought it would be better if the words "strainer" and "aerator" were used in describing such apparatus. Nitrification is a word very often used in connection with these matters, but is often misused so as to be almost equivalent to the term purification. Nitrification is the term given to the conversion of ammonia into nitrous and nitric acids by

organisms, and ought not to be applied to the breaking down of the organic nitrogenous matter into ammonia. There were some twenty or thirty organisms known to bring about nitrification, and some or all of these live and move and have their being in the aerators, but they were totally distinct from the organisms which had the effect of breaking down the original matter in the strainer. The initial process might be called hydrolysis, or the resolution of the complex organic compounds into simpler ones, without the addition of oxygen from the air. This breaking down of the solid fœces does not take place readily under ordinary circumstances, owing to the fact that it contains compounds like indole and skatole, which are antiseptic in their action, and which are secreted during the process of digestion in sufficient quantity to bring that process to a standstill. An analysis of focal matter shows that it consists of a considerable quantity of undigested food, in addition to cellulose and woody fibres which are not easily digested by man. The natural enzymes of the human system, or adventitious bacteria, would complete this digestion and render a large portion of the solid foeces quickly soluble if the antiseptic compounds were removed. Dilution with water in sewers and cesspools, and still better in these straining tanks, will remove these antiseptics and permit of further digestion. Even cellulose, paper and straw can similarly be rendered soluble by organisms provided no retarding antiseptics are present; and these newer processes of preliminary sewage treatment, as distinguished from precipitation, seem to be capable of explanation on these lines, the final conversion of the ammonia and ammonium compounds into nitrates being effected in the aerators or so-called coke-breeze filters.

Mr. A. R. BINNIE (Chief Engineer to the London County Council) said that he had been engaged for some years in studying how to dispose of 180,000,000 gallons of crude sewage per day, and that by the method of precipitation adopted 2,000,000 tons of sludge, containing about 200,000 tons of absolutely dry solid matter, are abstracted from this crude sewage and sent to sea every year. There were still, however, three to six grains of solid sewage matter per gallon in the effluent, and he, in conjunction with the Chemist to the Council, had tried experiments with a view to discovering the best mode of removing these, as well as a portion of the dissolved organic matter. In filters of the general description the water stood at two, three, to five feet above the filtering materials, which latter hardly ever got any aeration whatever. They were told that impurities consisted largely of organic matter, and that oxygen was necessary to effectually obviate its harmful effects. Sir Joseph Bazalgette had tried the experiment of oxygenising sewage by atmospheric air, but the effect of it had very little value, and the result of experiments had shown that it was necessary to bring the sewage into contact with the air under peculiar circumstances. As an engineer he had heard of nitrifying organisms, and enquiries to his bacteriological friends elicited the fact that these organisms were of peculiar habit

and could not be cultivated in the ordinary media. The experiments of himself and the Chemist to the Council were directed to finding out the best means of dealing with the effluent of the sewage, and after nine months' work they had come to the conclusion that filtration through coke was the best. The filter was composed of ordinary drain tiles covered with coke, and six inches of sand, the latter not for filtration purposes, but to keep the coke from floating at the top of the tank. The filter was filled and allowed to stand for a few hours, the water being then drawn off. In doing this a vacuum was created, and by atmospheric pressure the whole of the medium was thoroughly and rapidly aerated. The effluent after this treatment was absolutely unimpeachable, being clear and free from smell. But in observing the outlet drains it was at once apparent that the work was not complete. Nature was at work still, and the drains were a beautiful sight, being almost entirely coated with Vorticilla; yet the Engineer and the Chemist could and did by various processes remove the dead and effete matter, and render the effluent exceedingly pure.

The general result of his experience was that he did not think that any system of filtration, however perfect, would remove and get rid of the 2,000,000 tons of sludge, or the 200,000 tons of dry solid matter; and although the filters no doubt marvellously improved the effluent from the precipitation channels, yet he feared that even the filters themselves would require to be cleansed, as among the two to six grains of solid matter in suspension in the effluent, there was a certain amount of mineral matter which deposits itself as sticky mud on the upper or sand surface of the filter.

Mr. W. C. SILLAR (London) contended that considering the prominence now given to agricultural distress, the utilization of the manurial wealth contained in town sewage should be taken in conjunction with the subject under discussion which, judging from the terms of the paper read, seemed confined to its destruction merely. It was now no longer a matter of theory but of admitted fact that town sewage can be so treated as to preserve this manurial wealth, and Sir Douglas Galton knows this, as he has himself used it on his farm for several years in succession.

THE INFLUENCE OF SUBSOIL-WATER ON HEALTH.

BY S. MONCKTON COPEMAN, M.A., M.D.Cantab., M.R.C.P.

Lecturer on Hygiene and Public Health, Westminster Hospital.

Read at a Sessional Meeting, February 12th, 1896.

WHEN requested to open a discussion on the Influence of the Subsoil-Water on Health, I felt that it would be ungracious to refuse the invitation, seeing that when writing on this question some time ago, I had taken the opportunity of making myself as fully acquainted as possible with the literature of the subject. At the same time, however, I think it only right to state that it is unfortunately not within my power to lay before you anything of an original nature, for the reason that I have had, I regret to say, neither the time nor opportunity of carrying out research work in this direction.

Still it may possibly be open to question as to whether this very fact is altogether a disadvantage in the case of the opener of a discussion, who will, for this reason, perhaps, be likely to take a more thoroughly wide and impartial view of the matters under consideration than is altogether possible to a worker who has devoted his energies to the elucidation of one particular section of a subject, which under these circumstances, as I know from my own experience, is liable to appear of greater relative importance than by other persons may be considered to be quite justifiable.

Just as the drill sergeant "sizes" his men and ranges them in line for inspection by his superior officer, so, as it appears to me, a useful purpose may be served by a marshalling of the various theories, facts, and I might almost add, fancies, which from time to time have been advanced by observers who have carried out investigations relating to the subject matter under discussion; at the same time indicating, as far as may be in my power, the various points which either have as yet not received their due share of attention, or concerning which at present it has not been possible to arrive at any satisfactory conclusions.

To Pettenkofer is due the credit of having been the first to

direct attention, by his important investigations, to the subject of the subsoil-water in its relation to disease. In this connection it is necessary to distinguish between the amount of water mixed with air which is present in the interstices of the soil, known as "moisture," and the continuous subterranean lake or sheet of water found in most soils at varying depths from the surface, known as "ground-water." Pettenkofer defines this ground-water as that condition in which all interstices are filled with water, so that, except in so far as its particles are separated by solid portions of soil, there is a continuity of water.

The amount of "moisture in the soil" depends on its power of absorbing and retaining water, supplied by the rainfall, or derived from the ground-water below. It would appear that wetting of the soil, when due to a rise of ground-water, will conduce to active putrefaction in the deep layers, while the superficial layers remaining permeable, the products of decomposition can readily make their way to the surface of the earth, whereas when the wetting of the soil is due to the rainfall the conditions will be different.

This continuous sheet of water, termed "ground-water," is found below the surface of the soil, at depths which vary very considerably in different localities, as occasionally it may reach to within a few inches of the surface, while in other cases it may only be met with at a hundred or more feet below it. This difference in level will depend on the permeability of the soil, on the nature and inclination of the strata below the surface, whether loose or compact, and on the ease or the reverse with which the water can flow away to some outlet in springs, rivers, or the sea. The water is in constant movement in its endeavour to reach such outlets, and the variations in the level of the ground-water caused by such flow is best studied by taking measurements of the level of water in wells, as has been done in a most exhaustive manner by Pettenkofer, Fodor, Baldwin Latham, Adams, and others, who have insisted strongly on the importance of such variations of level of the ground-water, as constituting a weighty factor in the etiology of certain diseases, especially cholera, enteric fever, and diphtheria.

Fodor found that at Buda-Pesth such variations were regulated over the greater part of the city by the varying level of the Danube, the greatest fluctuations being found in the wells nearer the river; while on the other hand, the greater the distance from the Danube the smaller were the variations of the water level, until at the outer limits of the city they almost entirely disappeared.

Although the level of the ground-water is thus constantly changing, the difference between its highest and lowest levels