Unless, under exceptional circumstances, it is most undesirable to fill up any hollow or tank in the vicinity of any well from which drinking water is obtained. It may possibly be found the lesser of two evils to fill up small tanks or hollows in the interior of a bazaar with refuse, as these are frequently in an undescribable state; the charge made by a Municipality for doing this should, however, be so adjusted as to admit of the surface being well covered in with earth, which must, in all cases, be insisted on. If no charge is made, and no depôt for the refuse selected, it will be found that the cartmen will sell it by the cartload to irresponsible persons, when reasonable precautions as to covering in with earth and selection of site are not possible, the consequence being that innumerable breeding-places for flies are well distributed throughout the heart of a densely populated neighbourhood, in places where earth has been from time to time excavated for building huts. CHAPTER IX. BIOLOGICAL SYSTEM FOR THE DISPOSAL OF NIGHT-SOIL. Since this chapter was written, some 12 years ago much research work has been carried out in 1906. This was in India first systematised by Dr. Fowler in his report on “Septic Tanks in Bengal” and has been carried on by Major Clemesha, I.M.S., Sanitary Commissioner, Bengal, whose work on “Sewage Disposal in the Tropics” published by Messrs. Thacker, Spink & Co., Calcutta, is a most useful one and should be consulted by those interested in the subject. In the present state of knowledge of the science, it would be unsafe to discharge the effluent into a water-supply of small volume used for drinking purposes below the point of discharge, or in fact into any water which may be a potential source of water-supply, unless it be first sterilised. This can be easily and economically done with chloride of lime. In dealing with the resultant liquid of bacteriological treatment it is safest to consider it as a possible source of danger, and to discharge it either into the storm-water drains of a town, on land for irrigation purposes, for which it is most valuable, or into a large volume of running water, as circumstances admit of. The great advantage of bacteriological treatment of night-soil, and one which it is impossible to overestimate, is, that it enables the excreta to be disposed of when fresh, eliminates the necessity of stale night-soil being carted through crowded thoroughfares at a very low rate of speed, and consequent danger of the food and water-supply of the people being contaminated by the germs of disease conveyed by flies, or blown on in the dust. Latrines can be constructed over septic tanks, the home of the anærobic bacilli, where the excreta at once passes in, or dumping septic tanks can be worked at the night-soil depôts, where the stuff is at present collected, as at Darjeeling.