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A practical application of this theory is made in the various forms of sewage irrigation. It is known that if, whether by direct flow at the surface or by escape from pipes laid a short distance below the surface, the application of sewage is not too great, and is sufficiently intermittent, suitable soils become charged with scavenger bacteria at increased depths, and the power of purifying sewage-that is, the population per acre that may be served—is increased proportionately. This theory, that scavenger bacteria are active only in the upper layers of the soil, answers the question so often asked: "Why, if filth can safely be delivered into pipes lying a few inches under the surface, may it not as safely be delivered into cesspools or filteringwells leaching into the lower strata of the soil?" Filth delivered at or near the surface is immediately subjected to the action of the scavenger bacteria, and is destroyed by putrefaction and nitrification, as are its infective microbes, while that delivered at a depth where sufficient air is not present is subjected to a decomposition of another and possibly dangerous character, the multiplication of its infective microbes being favored in part, perhaps, by the character of this decomposition and in part by the absence of scavenger bacteria. If, as is altogether probable, as in fact seems to have been clearly demonstrated, ground-water flowing through or near privy-vaults, cesspools and the graves of cemeteries, is liable to infection from the sources indicated, that infection constitutes a menace to all who may become liable to infection from the use of that water as a beverage, and at times, perhaps, by exhalations from it.

It is clear, therefore, that while the water falling from the heavens on the surface of the ground does not, as a rule, carry dangerous elements to the ground-water, and though sewage discharged with proper precautions and with sufficient intermission on to the surface can contribute only a purified addition to the water of the sub-soil, and while both of these processes may be carried on systematically without danger to health, any method of disposing of liquids fouled with organic wastes which delivers them unpurified into the sub-soil, as well as the deposit of the bodies of the dead or of masses of filth at any considerable distance below the surface, is a source of danger constantly to be apprehended.

Whether or not the theory on which this opinion is based is destined to withstand the ultimate investigation of bacteriologists, the results for which it seems to account are confirmed by all experience

and observation that have come to the knowledge of sanitarians. The conclusion is not to be doubted that so far as infectious diseases of a zymotic character are concerned, we have nothing to fear from groundwater if we keep it pure, and we have everything to fear if we allow it to become impure. The practical results of this conclusion must be that the greatest attention should be paid to the manner in which we dispose of our liquid wastes. If we are obliged to deposit them in receptacles in the ground, these should be absolutely tight—not probably tight, but as tight as a bottle.

If we convey them from our houses through drains connected with sewers, every portion and every joint of the drains and of the sewers to above the greatest height ever reached by the flow, must be absolutely tight. Drains and sewers are always laid, in our climate, at a depth beyond which the purifying action above referred to ceases, and the same objection exists to the escape of their contents into the ground-water as would attend the delivery of the mouth of the drain in a brook. The communication and contamination may be less direct, but it is equally positive. It is hardly necessary to say that in the construction of house drains and sewers, as ordinarily laid, even with the best materials, and under the best specifications, but with insufficient inspection, leaking joints are not a rare exception, and that, while the great volume of the flow follows the drain to its outlet, its oozings along the route are sufficient to jeopardize the safety of the community.

I would be very far from intimating that it is not generally the wisest course to provide communities with an abundant supply of water delivered into houses, but I can conceive of a condition where this is not necessary for the best sanitary results. In a town where there are no cesspools and no privy-vaults, where there are no interments within the water-shed, where all drains and sewers are so absolutely tight as to insure the ground-water against contamination by sewage, and where no impurity can in any way reach the sub-soil, there seems to be no reason why ground-water may not be perfectly safe for domestic use.

The relations of ground-water to malaria, or fever and ague and neuralgia, are in one sense too well known to need discussion. In another sense, they are too little known for accurate discussion to be possible. We know very well that in the great majority of cases, where malaria attends an undue moisture of the soil, it may be

removed, for good and all, by suitable underdrainage. But we know of other cases, as in the dry plains of the Far West, where nothing approaching a swampy condition ever exists, where even a light shower of rain may produce serious malarial conditions. All that can be said positively is that most of us who have a practical interest in malaria, live subject to the undue moisture of soils at the East and not to the arid sources of malaria in the Far West; and that our practical remedy for this scourge is to withdraw the water of saturation to a sufficient depth to prevent the development of the malaria microbe in the surface soil.

9

MEMORANDUM AS TO LIGHTNING

CONDUCTORS.

BY PROF. C. F. BRACKETT, PRESIDENT STATE BOARD OF HEALTH.

In what follows no argument will be offered to show the general utility of lightning conductors. It is assumed as established by theory and confirmed by experience that they may be made to afford a good degree of security against the destructive effects of lightning. The practical questions which will be briefly treated relate to the material to be employed and to the proper insulation. Neither of these questions can be quite so easily answered as was formerly believed, for the advance in electrical science has discovered complicated relations which were quite unknown to Franklin and his contemporaries.

Franklin showed that the lightning flash is of the same general character as the discharge spark of a Leyden jar, and he compared the thunder cloud to one of the coatings of the charged jar and the earth to the other, while the intervening air represented to his mind the glass or non-conducting substance of the jar. He also knew that a charged jar can be quietly discharged by connecting its outer coating to the earth and presenting the pointed end of a metal conductor, also connected to the earth, to the knob. Hence, he concluded that metallic conductors, having their pointed extremities well above the highest portions of a dwelling or other structure, and in good connection with the moist earth, would quietly discharge the impending cloud and so protect the structure from damage.

A plain, continuous iron rod, fulfilling the conditions here mentioned, will no doubt often afford complete protection, yet it is not to be denied that it sometimes happens that notwithstanding the presence of such conductors, buildings are struck. Ships at sea have been struck upon deck, even though the masts were furnished with continuous conductors in good connection with the water.

The

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