-----+---------------------------------- | SAMPLING POINT NO. +------+------+------+------+------ | 1 | 2 | 3 | 4 | 5 +------+------+------+------+------ 1913 | 15.2 | 14.4 | 16.3 | 16.8 | 26.8 1914 | 7.0 | 5.7 | 6.0 | .... | 11.6 -----+------+------+------+------+------ In every case there was persistent diminution in the number of _B. coli_ with increase of contact period. Determination of the bacterial count on nutrient agar showed that, in several experiments, the aftergrowth had commenced, and in some instances there was evidence that the second cycle was partially complete i.e. the number had reached a maximum and then commenced to decline. The time required for the completion of the two cycles, comprising the first reduction caused by the chlorine, the increase or aftergrowth, and the final reduction due to lack of suitable food material, is dependent upon several factors of which the dosage and temperature are the most important. With a small dosage the germicidal period is short and the second phase is quickly reached; with large doses, the second phase is not reached in forty-eight hours; the higher the temperature the quicker is the action and the development of the aftergrowth. These statements refer only to the bacteria capable of development on nutrient agar. The _B. coli_ group behaved differently and persistently diminished in every case. If _B. typhosus_ acts in a similar manner to _B. coli_, the laboratory experiments show that aftergrowths are of no sanitary significance and can safely be ignored, but as the results obtained in practice are contradictory to the laboratory ones, the matter must be regarded as _sub judice_ until more definite evidence is available. It is common knowledge that samples of water from "dead ends" of distribution mains show high counts and much larger quantities of _B. coli_ than the water delivered to the mains. This is another phase of aftergrowth problem that often causes complaints and can only be eliminated by "blowing off" the mains frequently or by providing circulation by connecting up the "dead ends." One extreme case of this description might be cited. A small service was taken off the main at the extreme edge of the city to supply a Musketry School two miles away and was only in use for a few months in the summer season. This service pipe delivered water containing _B. coli_ in a considerable percentage of the 10 c.cm. samples and in a few instances in 1 c.cm., although the water delivered to the city mains never exceeded 2 _B. coli_ per 100 c.cms. and averaged about one-tenth that quantity. No epidemiological records of the effect of this water are available because it was put through a Forbes steriliser before consumption.