During the years 1909-10-11, when practically the whole of the city supply was filtered, the average typhoid death rate was 18, but when the water was also chlorinated, in 1914-15-16, the rate was only 7, a reduction of 61 per cent.
The figures in [Table XXXII] show that the Torresdale filters, during 1915-16 were unable to adequately purify the water and that chlorination was necessary.
TABLE XXXII.—CHLORINATION OF FILTER EFFLUENTS
| (Torresdale) | ||||||||||||
| Oxygen Con- sumed. | Colour. | Tur- bidity. | Bacteria Per Cubic Centimeter. | B. coli communis Per Cent Positive Tests. | Added Chlorine Parts Per Million. | |||||||
| Untreated. | Treated. | Untreated. | Treated. | |||||||||
| Gela- tine. | Agar. | Gela- tine. | Agar. | 10 c.cms. | 1 c.cm. | 10 c.cms. | 1 c.cm. | |||||
| 1915 | 1.70 | 12 | 0.6 | 141 | 30 | 28 | 14 | 66 | 24 | 5 | 0.3 | 0.18 |
| 1916 | 1.90 | 12 | Nil. | 88 | 23 | 38 | 11 | 49 | 16 | 7.4 | 1.9 | 0.15 |
In [Diagram XI] the typhoid death rates of Columbus, Ohio, and New Orleans are shown to exemplify conditions that have not been improved by chlorination. The endemic condition of typhoid in Columbus was brought to an abrupt conclusion by the installation and operation of the softening and filter plant in September, 1908, and no further reduction followed the introduction of chlorination in December, 1909.
DIAGRAM XI
TYPHOID IN COLUMBUS AND NEW ORLEANS
