Some deep wells in the chalk are liable to contamination. The pollution may gain access to the wells by means of fissures or “swallow-holes” in the water-bearing stratum, and, through these defects, micro-organisms and organic matter may find their way into the water supply of a town from points many miles distant. The risk of chalk waters becoming contaminated is daily growing more probable: quick and cheap transit is responsible for an exodus from the town to the country which serves as a gathering ground for water supplies; and the chalk uplands and countryside, which formerly were sparsely populated, are in many places becoming covered with collections of houses and small villages, whose only method of sewage disposal is by means of cesspools into the chalk on which the houses are built. If the chalk is sound and unfissured, this method of sewage disposal is not harmful to distant water supplies; but, given a fissure or swallow-hole, the intestinal micro-organisms and organic matter from some outlying village, may make the water from a deep well some miles away unfit to drink. I know at present of five important wells in the chalk in different parts of England, which are, in this manner, liable to intermittent and undoubted faecal contamination; but, in only two of these places are means taken to purify the water before it is distributed to the consumers. A typhoid carrier or a case of enteric fever might distribute bacilli to a distant town through some imperfection in the stratum, and the consequences, without doubt, would be very disastrous; yet probably there are many towns in the country which take the risk of such an epidemic.