It is, as a rule, during the winter months that the largest number of bacteria are present in the filtered water, and it is therefore of especial importance that during this season, when the raw river water is generally richest in bacterial life, and when, therefore, the filters are most taxed and the consequences of frost are most to be apprehended, that those entrusted with this responsible task should be unremitting in their endeavours to obtain a good filtrate. That waters submitted to exhaustive natural filtration, such as those derived from deep wells sunk into the chalk, and usually almost entirely devoid of bacterial life, may at times become the carriers of disease has been proved by the disastrous outbreak of typhoid fever which occurred some years ago at Worthing. This town has long been supplied with water of the very finest quality for dietetic purposes, and nothing could have been more unexpected than this most fatal epidemic. It must, however, be borne in mind that such deep-well waters are not necessarily immaculate, for in the event of any fault in the water-bearing strata occurring, the filtration becomes inefficient, and the water may then, as in the case of Worthing, be the bearer and disseminator of zymotic disease. The bacteriological methods for the examination of water, although when first introduced but a few years ago were lightly looked upon, and by many opposed, have now become of paramount importance in all questions of water-purification. The immense mass of evidence of a purely bacteriological character which was taken, and indeed required by the Royal Commissioners of 1893 on the London water-supply, indicates clearly enough the change which has taken place in the public estimation of the value of these methods; and it is highly significant that in their report the Commissioners lay stress upon the importance of extensive storage and efficient filtration, two factors the meaning and worth of which rest almost entirely on the results of bacteriological research. Cholera is not, however, the only water-carried disease which has borne eloquent testimony to the services rendered by the efficient purification of public water-supplies. The experience of the State of Massachusetts in America, in regard to typhoid fever and drinking-water, is also exceedingly instructive.