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We have seen that a regular supply of pure air-in other words, efficient ventilation—is required to remove the excreta of the lungs and the volatile products of the skin. The solid and fluid excreta from the bowels and the kidneys ought to be as rapidly and as completely removed as the gaseous impurities.

It is highly probable that to barbarous and inefficient modes of removing the excreta of men and of animals we must partly trace the great prevalence of disease in the middle ages, and there is no doubt that many the diseases now prevailing in our large towns are owing to the same

When men live in thinly populated countries, following, as they will then do, an agricultural or nomade life, they will not experience the consequences of insufficient removal of excreta. The sewage matter returns at once to that great deodorizer the soil, and fertilizing it, becomes a benefit to man, and not a danger. It is only when men collect in communities that the disposal of excreta becomes a matter literally of life and death, and before it can be settled the utmost skill and energy of a people may be taxed.

The question of the proper mode of disposal of sewage has been somewhat perplexed by not keeping apart two separate considerations. The object of the physician is to remove as rapidly as possible all excreta from dwellings, so that neither air, water, nor soil shall be made impure. The agriculturist wishes to obtain from the sewage its fertilizing powers. It is not easy to satisfy both parties, but it will probably be conceded that safety is the first thing to be sought, and that profit must come afterward.



Amount of the Solid and Fluid Excreta. The amount of the bowel and kidney excreta vary

in different persons and with different modes of life. On an average, in Europe, the daily solid excreta are about 4 ounces by weight, and the daily fluid excreta 50 ounces by measure for each male adult. Women and children pass rather less. Vegetable pass more solid excreta than animal feeders, but this is chiefly owing to a large proportion of water. Taking all ages and both sexes into

Mr. Fawcus's experiments on Bengalee prisoners give an average bowel excretion of 12 ounces, and in Bombay Dr. Hewlett found the alvine discharges to be quite as large.

consideration, we may estimate the daily amount per head of population in Europe at 24 ounces of fæcal, and 40 ounces of urinary discharge. A population of 1,000 persons would thus pass daily 156 lb of solids and 260 gallons of urine, or in a year 25 tons of fæces, and 91,250 gallons (14,646 cubic feet) of urine. Letheby gives the mean amount per head as 2.784 ounces of fæces and 31.851 ounces of urine. In a mixed population of 1,000 persons of different sexes and ages, Letheby has calculated that the daily discharge of the whole town will be 2,266 lb avoir. of urine and 177.5 lb of fæces.

Frankland estimates the mean daily amount per head as 3 ounces of fæces and nearly 40 ounces by measure of urine. In adult males the quantity of nitrogen daily discharged by the bowels and kidneys amounts to from 250 to 306 grains, representing 304 and 372 grains of ammonia. Taking the whole population, however, the amount must be considerably less than this. Dr. Parkes calculated it as 153 grains of nitrogen, and Letheby gave it as 155.8 grains, or from 186 to 189 grains of ammonia, i.e., the mean excretion of all the population is very nearly half the excretion of the adult male.

Decomposition of Sewage Matter. Fresh healthy fæcal matter from persons on mixed diet, unmixed with urine, has an acid reaction, and this it retains for a considerable time; it then becomes alkaline from ammonia. If free from urine, it usually decomposes slowly, and in hot weather often dries on the surface, and subsequently changes but little for some time. The urine, when unmixed with fæcal matter, also retains its natural acidity for a variable number of days, sometimes three or four; sometimes eight or ten, or even longer, and then becomes alkaline from ureal decomposition. When the fæces and urine are mixed, the formation of ammonium carbonate from ureal decomposition is much more rapid ; the solid excreta seem to have the same sort of action as the bladder mucus, and the mixed excreta become alkaline in twenty-four hours, while the separate excreta are still acid. And in its turn the presence of the urine seems to aid the decomposition of the solid matter, or this may be perhaps from the effect of the fluid, as pure water seems to act almost as rapidly as urine in this respect. Pappenheim' states that the absorption of oxygen by the fæces is greatly increased when urine is added. When the solid excreta and urine are left for two or three weeks, the mixture becomes usually extremely viscid, and this occurs, though to a less extent, when an equal quantity of pure water takes the place of urine. The

viscidity is prevented by carbolic acid.

When the solid excreta (unmixed with urine) begin to decompose, they give out very fetid substances, which are no doubt organic; hydrogen sulphide is seldom detected, at any rate by the common plan of suspending paper soaked in lead solution above the decomposing mass. When heated, a large quantity of gas is disengaged, which is inflammable, and consists in great measure of carburetted hydrogen. When (instead of being dry) urine is present, ammonia and fetid organic matters are disengaged in large quantity. When water is also present, and if the temperature of the air is not too low, not only organic matters but gases are given out, consisting of light carburetted hydrogen, nitrogen, and carbon dioxide. Hydrogen sulphide can be also disengaged by heat, and is almost always

1 Handb. der. San. Pol., 2d edit., Band i., p. 72. VOL. II.-2

found in the liquid, usually in combination with ammonia, from which it is sometimes liberated and then passes into the air.



While all will agree in the necessity of the immediate removal of excreta from dwellings, the best modes of doing so are by no means settled. The fact is that several methods of removing sewage are applicable in different circumstances, and their relative amounts of utility depend entirely on the condition of the particular place. The different plans may be conveniently divided into

1. The water method.

2. The dry methods. Before noticing these plans, it will be convenient to make a few general observations on sewers.

SEWERS. Sewers are conduits employed to remove waste water and waste products suspended in water from houses, or to carry away rain. Among the waste products may be the solid and liquid excreta of men and animals, or the refuse of trade and factory operations. Or sewers may be used merely for the conveyance of dirty house water, without the admixture of excreta or trade refuse.

It is quite impossible that any town or even any single large house can be properly freed of its waste house water without sewers, and in a more or less perfect condition they are to be found not only in all modern, but in most ancient cities. Originally, no doubt, they were mere surface channels, as they are still in many towns; but for the sake of appearance and inoffensiveness, the custom must have soon arisen of placing them underground, nor in modern towns could they now be arranged otherwise. In some large towns there are even hundreds of miles of sewers, constructed often with great skill and science, and they serve in some instances as the channels not only for rain, but for natural streams which have been enclosed.

The sewers form thus in the subsoil of towns a vast network of tubes, connecting every house, and converging to a common outlet where their contents may be discharged.

In some towns the sewers carry away none of the solid excreta, though probably urine enters in all cases. In most towns, however, solid excreta, , in greater or less quantity enter, owing especially to the prevalent use of water-closets, or to the drainage of middens and manure heaps.

Whether the solid excreta pass in or not, the liquid in the sewers must always contain either suspended or dissolved animal and vegetable matters derived from the refuse of houses. It is generally warmer than the water

| Dr. Corfield's work (A Digest of Facts relating to the Treatment and Utilization of Sewage, by W. H. Corfield, 2d edit., 1871) will be found to give a good summary of this subject. See also Report of a Committee appointed by the President of the Local Government Board to inquire into the several modes of treating Town Sewage, London, Eyre & Spottiswoode, 1876 ; see also“Die Menschliche Abfallstoffe," von Dr. Ferd. Fischer, Supplement zur Deutschen Viertelj. f. Offt. Gesundh., 1882.

of streams, and is of no constant composition ; sometimes it is very turbid, and highly impure ; in other cases it is hardly more impure than the water of surface wells. The suspended matters are, however, generally in larger proportion than the dissolved.

In some cases the sewer water is in greater amount than the water supplied to the town and the rainfall together. This arises from the subsoil water finding its way into the sewers.

One ton of London or Rugby sewage contains only from 2 lb to 3 lb of solid matter (Lawes).'

The average composition of sewer water in towns with water-closets is, organic matter, 27.72; nitrogen, 6.21 ; phosphoric acid, 1.57; potash, 2.03 grains per gallon."

The Rivers Pollution Commissioners give 7.28 grains of organic nitrogen per 100,000 parts, or 5.41 grains per gallon; the mean amount of ammonia is 6.703 per 100,000, or 4.695 grains per gallon.

Under the microscope, sewer water contains various dead decaying matters, and in addition multitudes of Bacteria and amoebiform bodies, as well as some ciliated infusoria, especially Paramecia. Fungi (spores and mycelium) are seen, but there are few Diatoms or Desmids, and not many of the higher animals, such as Rotifera.

A controversy is still going on, whether the solid excreta ought to be admitted into the sewers. The point is virtually practically decided in many towns in this country by the general use of water-closets, which cannot now in these towns be superseded by any plan yet proposed. It is, however, quite an open question, whether, if all the arrangements could be commenced de novo, the admission of the solid excreta would be proper.

The arguments for and against this view will presently be stated.

Whether the solid excreta are allowed to pass in or not, it is clear that the dirty water of the sewers must in some way be disposed of. It is in every case more or less impure, containing animal and vegetable substances in a state of commencing decay, which passes readily into putrefaction. The readiest mode of getting rid of it is to pass it into streams, where it is at once subjected to the influence of a large body of water, and where the solid matters become either slowly oxidized, or form food for fishes or water plants, or subside. Although from an early period streams were thus contaminated and their water originally pure was thus rendered unfit for use, it is only lately that a strong opposition has arisen to the discharge into streams. This is owing partly to the greater pollution and nuisance caused by the more common use of water-closets and the largely increasing trade of the country, which causes more refuse to be sent in, and partly to the evidence which has been lately brought forward of the diseases which are caused by drinking water made impure in this way. To prevent the nuisance and danger caused by the pollution of streams, many actions at law have been brought, and in some cases special Acts of Parliament have forbidden the discharge of sewer water into certain rivers until after efficient purification. The Rivers Pollution Act of 1876 now deals with the question, its provisions having come into operation on August 15, 1877.

1 For the composition of sewer water see Way, Second Report of Common Sewage of Towns, 1861, p. 69 et seq.; Letheby, The Sewage Question, 1872, p. 135 ; Report on Torn Sewage, 1876; Rivers Pollution Commissioners' Report.

* Letheby, op. cit., p. 138.

Up to a certain point, there would probably be a general agreement as to the principle on which this difficult question should be dealt with. Animal substances in a state of decay can be best prevented from contaminating the air, the soil, or the water of streams, by imitating the operations of nature. In the endless cycle of physical change, decaying animal matters are the natural food of plants, and plants again form the food of animals.

It so happens that, with the exception of some mineral trades, the waste products of which are hurtful to agriculture, many of the substances contained in the sewer water of our towns are adapted for the food of plants, and we seem on sure ground when we decide that it must be correct to submit these matters to the action of plant life, and thus to convert them from dangerous impurities into wholesome food.

The difficulty is, however, with the application of the principle, and at the present moment there is the utmost diversity of opinion on this point. It seems, however, that we may divide the opinions into two classes. According to one opinion, the proper mode is to bring the waste water of towns, when it contains fertilizing matters, at once to the ground, and after the arrest of substances which may block the pipes, to pour it over the land in such a way as may be best adapted to free it from its impurities, and to bring it most rapidly and efficiently under the influence of growing plants.

The other opinion objects to this course on two grounds : first, that the substances are not brought to the ground in the most convenient form for agriculture, and also that the plan entails evils of its own, arising from the immense quantity of water brought upon the land and from the difficulty of efficient management. The advocates of this second view would, therefore, use some plan of separating the impurities of the water, and would then apply them in a solid form to the land, or use them for some other purpose, as in General Scott's plan of adding the materials for cement and then making this substance. The purified water would then be filtered through land, or passed into streams, without further treatment.

In the case of the sewage water containing materials not adapted for agriculture, both parties would deal with it in the same way, viz., purify it by chemical agencies or filtration, and then allow the water to flow off into streams, while the solid products would be disposed of in the most con

These general views apply to any sewer water, whether it contains solid excreta or not, although if these excreta can be perfectly excluded the sewer water is less offensive. It has hitherto been often poured into streams without previous purification, though now this practice is prohibited by law, with certain reservations.

The sewers of a town are for the most part used also to carry off the rainfall, and, indeed, before the introduction of water-closets, they were used only for this purpose, and for taking away the slop and sink water of houses. In countries with heavy rainfall, and in this country in certain cases, the rainfall channels are distinct from the sewers, and the outfalls may be in an entirely different direction. This is sometimes called the "separate system."

REMOVAL OF EXCRETA BY WATER. This is the cleanest, the readiest, the quickest, and in many cases the most inexpensive method. The water supplied for domestic purposes,

venient way.

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