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4. POLLUTION FROM HOUSEHOLD SEWAGE..

It is obvious that infection of the soil by decaying organic matters is liable to vitiate subterranean waters and render them unsafe for drinking and culinary purposes. Depreciation of a water supply by household or domestic sewage is one of the worst forms of pollution. It not infrequently happens that waters fouled in this way contain infectious germs, and the necessity for exercising great care with reference to them is not only important but urgent. All waters, even the purest, contain some organic matter, but when it exceeds a certain limit, or has undergone putrefactive changes, the drinking of such water is attended with risk and even with danger. This is especially the case with reference to human excreta. Professor Mallet, of the University of Virginia,* has called attention to the fact that no known poison, in the diluted state, will produce the effects which have been traced to drinking water contaminated with human excreta; in fact, there seems to be no dilution which can make such polluted waters safe. They are the culture fields for the germs of the most deadly diseases, such as cholera, typhoid fever and dysentery.

Dr. Frankland maintains that water once contaminated with excretal sewage, even if purified subsequently by filtration in the most perfect way attainable, if not positively dangerous, is still unsafe to be used. "There are," he says, "animal organisms existing in sewage matter so minute as not to be seen by the unaided eye, and we have reason to believe that they even exist outside the range of microscopic vision, and possess powers antagonistic to human life."

Dr. Macadam, of Edinburgh, who has paid great attention to the water question, says: "The line must be distinctly drawn between non-putrescent organic matter and that which is putrescent. Impregnations from household sewage form the most dreaded contamination, and yield waters which, though clear and sparkling, are yet most unwholesome and deadly."

It is true we cannot always prevent a certain quantity of household refuse from falling upon and penetrating the soil, but it is nevertheless a duty which we owe to the public health to reduce this source of pollution to a minimum. It will always be found that the increase in certain diseases is pari passu with the increased pollution of the water supply, no matter how abundant the flow of water may be. The annual death-rate in New Orleans from typhoid fever is only 16 in 100,000 of population. Why? Because sewage cannot pollute the water supply of the city, which is received principally from tanks or cisterns above ground filled with rain water. In Philadelphia, where the water supply is taken principally from the Schuylkill River, which drains a vast agricultural and manufacturing territory, and receives the influx of foreign matters from two large and growing cities, besides many smaller towns, and is known to be contaminated, the annual death rate from typhoid fever is said to have increased in a few years from 56 to 68, or 12.16 per cent. per 100,000 of population.

* Report of the National Board of Health.

It is a great error to suppose that infected matter is rendered innocuous by dilution with water. Dr. Mead Bolton, late assistant professor of bacteriology in the Johns Hopkins University, following up the experiments of Flugge, of Breslau, has shown* that the most dangerous microbes will not only live but multiply in the purest water when once introduced. The microbes of charbon, he says, will disappear in six days, but their spores, that is to say their eggs, will be preserved for twelve months. The microbes of typhoid fever have been observed to live in practically pure water for thirty days, and three months in water containing one grain of organic matter per quart of water. As to cholera bacilli, dirty water is a marvelous medium for their propagation and growth; and even in ordinary water it has been ascertained that they will live at least seven months.

PRECAUTIONS AND REMEDIES.

The precautions that are best suited to preserve water supplies from contamination, and the remedies most appropriate to restore purity when lost, either by ordinary causes, or by those that produce epidemic diseases, may be classified as follows:

I. EXCLUSION OF ORGANIC FILTH.

Nearly all natural waters hold in solution or suspension a larger or smaller proportion of organized matter, which determines, to a certain extent, their impurity and unfitness for domestic purposes. We shall divide the organic matter present in water into the living and dead-both having their origin in the animal or vegetable kingdoms. The dead animal matter, among the natural causes of contamination, consists of the bodies of fish, insects, infusoria, etc., as also the soluble nitrogenized compounds dissolved out of these by the water. The dead vegetable substances are the remains of water plants, portions of land plants, leaves of trees, etc., which, particularly in Autumn, are found in river water in considerable quantities. As the laws of vitality have no longer any control over these substances, they become decomposed and resolved into their component elements, which combine according to the laws of chemical affinities, and yield products complex in their chemical constitution, and of a more or less dangerous or unwholesome nature.

The living organisms of animal origin found in water are fish, infusoria, insects, etc.; of vegetable origin, water plants, and a variety of singularly organized atoms, invisible to the naked eye, known by the popular name of microbes, which are certain colorless algæ belonging to the family bacteriacæ. Insomuch as the living animal and vegetable productions are dependent upon the dead organic matter of the water for their sustenance, it follows that whereever living beings are found in water there must exist the requisite materials for their nourishment. Pure distilled water can neither sustain animal nor vegetable life. The existence of living organisms in water in larger nor smaller quantities, is an indication of the greater or less amount of soluble organic matter in

*Nouvelle Revue d'Hygiene.

the water, as also of its purity or impurity. When they exist in small quantities it follows, other things being equal, that the water must be pure. These living

beings, animal and vegetable, act as depuratory, and we learn by their presence that there must exist the requisite amount and proper sort of food for their maintainance; hence their existence in water denotes a certain amount of soluble organic principles. We cannot but think, therefore, that the value of the information derived from microscopical observation of the organic impurities in water has not been heretofore sufficiently insisted on.

In

It is now agreed that the sewage matters of towns, including excretal and household wastes, however largely diluted, cannot with safety be allowed to flow into any source of water supply used for dietetic or culinary purposes. order to carry off such wastes a system of closed vessels or impermeable pipes should be provided, distinct from the storm water drains, to discharge the matter at a depot or outfall independent of any river or stream, except for a practically pure effluent. The discharge, directly or indirectly, of crude sewage into any source of water supply, however remote, is a constant concomitant of epidemic diseases, while a proportionate exemption from such maladies will invariably follow the removal of the pollution. A pure and abundant supply of water is cheap at any price, and "millions" to secure it, would be better than "millions for defence." I scarcely need add that all manufactories and trades should be required to clean their own waste; not, of course, to convert it into a chemically pure water, but simply to deprive it of its power to become a nuisance to others when discharged into a public water-way.

At the International Congress of Hygiene, which assembled in Paris during the Exhibition of 1889, there was an interesting debate on the pollution of rivers. The Congress decided that the pollution of water courses or rivers by the residue of factories should, in principle, be forbidden, and that polluted water from factories should not be allowed to flow into a stream until it had been proved to be absolutely free from all injurious substances. The congress was of the opinion that the most perfect method of purification was by irrigation. This, of course, must in certain cases be preceded by such mechanical and chemical processes as would render the water fit for agricultural purposes. It was related that many manufacturers had benefited by the application of this law, as in their efforts to prevent the pollution of water courses they had made discoveries enabling them to utilize waste products. The difficulty was with the smaller manufactories-not rich enough to take the necessary measThe congress further decided that where persistent resistance was displayed the authorities should themselves execute the work prescribed for the purification of water, and compel the persons interested to pay the cost.

ures.

2. PURIFICATION OF WATER BY ALUM.

The use of alum as a purifier of water seems to date back a long time. Particular attention was directed to its use by Jennet, in 1865, in an article published in the Moniteur Scientifique. He found that 2.3 grains of alum to a

gallon of water rendered it drinkable, even when it was quite full of foreign matter. The time taken for this clarification was from seven to seventeen minutes. Prof. Austin, of Rutgers College, N. J., states that the amount of alum used by Jennet is unnecessarily high, and in some experiments instituted to determine what is the practical minimum limit of alum that is needed to clarify New Brunswick hydrant water, he found that 1.2 grains was about as small an amount as it seemed practical to use to get a perfect separation of the impurities. Some waters, he thinks, may require less and some may require more ; but this is a matter very easily determined for any particular case which may arise. The great argument in favor of alum as a purifier of water is that it is cheap, can be obtained everywhere and is not highly poisonous.

3. FILTRATION FOR THE PURIFICATION OF WATER.

Chief among the subjects discussed at the Paris Congress, already referred to, was the purification of drinking water by artificial filtration, and some experiments were related which appear to show that noxious microbes may be removed, or at least rendered harmless, by certain methods of filtration. It was stated that guinea-pigs were inoculated with water which contained the microbe of anthrax, and that those inoculated with the water prior to filtration died with the usual symptoms of the disease, while those inoculated with the same water after filtration survived. A still more astonishing statement has been made by a London savant, viz.: That “a sufficiently careful filtration will remove most organic matters-among others, strychnia;" and it is said that the chemist who made this discovery was so sure of his facts that he drank, after filtration, a quantity of water in which, before it was poured into the filter, a poisonous dose of strychnia had been dissolved.

Filtration is no doubt an excellent practice, and one which, however it is accomplished, has at least the merit of rendering water more pleasing to the eye, if not to the palate; but it cannot be too widely known that some forms of filter do no more than this, and that water which is very bright and sparkling may yet contain noxious matter in solution. It would be well for the sanitarian, before extending his approval to any process of filtration, to understand explicitly the conditions which a perfect filter should be expected to fulfill, and to know that it has been subjected to adequate tests. Without this knowledge a mere belief in the efficacy of filtering may chance, in the long run, to prove a source rather of danger than of safety to the public. It is not sufficient to rely upon the sparkling limpidity or the refreshing sweetness of an effluent, because this will afford no security that the special characteristics on which the usefulness of the filter depends will be preserved in all future examples.

4. FILTRATION THROUGH CHARCOAL.

For many years charcoal held a high place as an efficient purifier of water. It has great power of absorption, but it is also capable of saturation. The experiments of Mr. Edward Byrne deserve, in this connection, particular

*"Institution of Civil Engineers," May 21st, 1867.

notice. He has shown that with a filter of animal charcoal weighing 41⁄2 pounds, through which only twelve gallons of water were passed in twenty-four hours, the purifying effect was equal to the removal of 551⁄2 per cent. of the organic matter from the first gallon. This gradually declined until at the fourth gallon only 1.33 per cent. were removed, and already at the eighth gallon the action was reversed, organic matter being given back to the water. It has further been proved, especially by the experiments of Dr. Chaumont, that a low organic life is speedily developed in water which has filtered through charcoal, and the same effect is produced in water by long contact with this material.

The Rivers Pollution Commission of England say in their fourth report, p. 220, that "the property which animal charcoal possesses of favoring the growth of low forms of organic life is a serious drawback to its use as a filtering material for potable water." The commission found that "myriads of minute worms were developed in the charcoal and passed out with the water." The utility of domestic filters for the purification of water intended for culinary or dietetic purposes, and the advisability or necessity of their universal adoption is strenuously insisted on by some persons and as firmly denied by others. There can be little doubt that filters are too frequently regarded as a kind of conjuring apparatus which will go on yielding to an indefinite extent pure water from dirty water, without receiving a tithe of the cleansing and attention which are bestowed on the rude sand beds of ordinary water-works. It would be well to remember that the success of any filter in the accomplishment of its legitimate work depends upon the frequency with which it is cleaned. No house filter should be used continuously for a longer period than two or three days without drawing off the contained water and allowing the air, which is much more destructive of organic matter than water, to pass freely through the filtering material for several hours. It would be well to have two filters and use them alternately every forty-eight hours. All filters in which the materials are enclosed between sides which are cemented or soldered into the case are to be avoided, as such filters are not capable of being easily cleaned.

5. FILTRATION THROUGH SAND AND GRAVEL.

From time to time considerable stir is made in scientific and popular papers and at sanitary meetings about some new device for purifying water, and consumers, terrified by the dismal pictures drawn of the condition of the town's water, frequently fall victims to sanitary "quackery," and purchase costly filters, the best of which are rarely more efficient than a common flower-pot filled with sand and gravel, while the worst are infinitely lower in the scale of utility. The simpler the construction the more effective generally will be the filter.

The artificial filtration of water on a large scale has become very general throughout Europe, where the water supply is taken from rivers, lakes or ponds. The main cause of the difficulties which have been encountered in this direction is the failure to obtain an economic system for such enormous volumes

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