Chlorination, by decreasing the load on filter beds, has enabled the rate of filtration to be increased in some cases. This increased capacity, which would otherwise have necessitated additional filter units, has been obtained without any further capital outlay. At Pittsburg (Johnson[5]) the rate of filtration, after cleaning, was increased 250,000 gallons each hour until the normal rate was reached; restored beds were maintained at a 250,000 gallon rate for one week. After the introduction of chlorination it was found possible to increase the rates more rapidly without adversely affecting the purity of the mixed filter affluents. _Hygienic Results._ Evidence as to the actual reduction of the number of such pathogenic germs as _B. typhosus_ in water supplies by chlorination is most readily found in the death rates from typhoid fever in cities that have no other means of water purification. In some cases this evidence is necessarily of a circumstantial nature; in others it is definite and conclusive. Some of the earlier results of the effect of chlorination on typhoid morbidity and mortality rates were compiled by Jennings[6] and others have been published by Longley.[7] These data have been brought up to date in Table XXXI and other statistics added. TABLE XXXI.--EFFECT OF CHLORINATION ON TYPHOID RATES AVERAGE TYPHOID DEATH RATE PER 100,000 POPULATION ----------------+-------------+--------------+--------------+----------- City. | Commenced | BEFORE USING.| AFTER USING. | |Chlorination.+-------+------+-------+------+ Percentage | |Period.|Rate. |Period.|Rate. | Reduction. ----------------+-------------+-------+------+-------+------+----------- Baltimore |June 1911 |1900-10| 35.2 |1912-15| 22.2 | 36 Cleveland |Sept. 1911 |1900-10| 35.5 |1912-16| 8.2 | 77 Des Moines |Dec. 1910 |1905-10| 22.7 |1911-13| 13.4 | 41 Erie |Mar. 1911 |1906-10| 50.6 |1912-14| 15.0 | 70 Evanston, Ill. |Dec. 1911 |1908-11| 29.0 |1912-13| 14.5 | 50 Jersey City |Sept. 1908 |1900-17| 18.7 |1909-16| 8.4 | 55 Kansas City, Mo.|Jan. 1911 |1900-10| 42.5 |1911-16| 14.2 | 66 Omaha, Neb. |May 1910 |1900-09| 22.5 |1911-16| 10.6 | 53 Trenton |Dec. 1911 |1907-11| 46.0 |1911-14| 28.7 | 35 Montreal |Feb. 1910 |1906-10| 40.0 |1911-16| 25.0 | 37 Toronto |Apr. 1911 |1906-10| 31.2 |1912-16| 7.8 | 75 Ottawa |Sept. 1912 |1906-10| 34.0 |1913-17| 17.0 | 50 ----------------+-------------+-------+------+-------+------+----------- The figures given in this table show the effect of chlorination only; no other form of purification was used during the periods given, except at Toronto where a portion of the supply has been subjected to filtration.