82 BACTERIA 



is helpful to classify these as pollutions at the source, in the 

 course, and at the periphery. Gathering-grounds are fre- 

 quently the locality of the pollution. The recent Maidstone 

 epidemic is an example. Here some of the springs supply- 

 ing the town with water were contaminated by several 

 typhoid patients. Frequently on the gathering-ground one 

 may find a number of houses the waste and refuse of which 

 will furnish ample surface pollution, which in its turn may 

 readily pass into a collecting reservoir or a well. Only re- 

 cently the writer investigated the cause of typhoid in a large 

 country house, and traced it to pollution of the private well 

 by surface washings from the stable quarters. Leakage of 

 house-drains into wells is not an infrequent source of con- 

 tamination. The same cause is generally operative in cases 

 of pollution of a water supply in its course from the source 

 to the cisterns or taps at the periphery, viz., a sewer or drain 

 leaking into the water supply. 



Water companies and those responsible for water supply 

 appear to hold the opinion that so long as there is sand 

 filtration or subsidence reservoirs it is unnecessary to con- 

 sider the gathering-ground or transit. But, as we have 

 seen, a frost may completely dislocate the efficient action 

 of a filter, and times of flood may prevent proper sediment- 

 ation ; then our dependence for pure water is wholly upon 

 the gathering-ground and source. Hence we find water con- 

 taminated at its source by polluted wells, by sewage-infected 

 rivers and streams, by drainage of manured fields, by in- 

 numerable excremental pollutions over the areas of the 

 gathering-grounds, and in transit by careless laying, poor 

 construction, bad jointing, and close proximity of water- and 

 drain-pipes. In the third place, we may get a water infected 

 at the periphery, in the house itself. Such cases are generally 

 due to one of two causes : filthy cisterns or suction. Cisterns 

 per se are more or less indispensable where a constant service 

 does not exist, but they should be inspected from time to 



