August 8, 1902.] 



SCIENCE. 



221 



chapters on sewage and water supplies and ice. 

 He very properly emphasizes the important 

 services rendered by the State Board of Health 

 of Massachusetts in solving some of the prob- 

 lems involved in the purification of sewage 

 by land treatment or intermittent filtration, 

 and the purification of water by slow sand 

 filtration. His description of the latter pro- 

 cess is very simple and clear, and while the 

 process is nearly, if not exactly, the same as 

 in the. purifying of surface waters which pass 

 through earth and become ground waters, we 

 believe that properly constructed filter beds 

 are an improvement on nature as there will 

 be no geological flaws which permit the pas- 

 sage of disease germs. We cannot subscribe 

 entirely to the author's views expressed on p. 

 239, regarding artificial processes of purifica- 

 tion of water supplies, especially the process 

 known in America as mechanical filtration, 

 and especially his paragraph on page 240 re- 

 lating to the hygienic efficiency of rapid me- 

 chanical filters. The importance of the sub- 

 ject demands a full presentation of the com- 

 parative efficiency of the natural, or slow, and 

 the rapid mechanical filters. Perhaps the 

 most recent and exhaustive discussion of this 

 subject will be found in Senate Document 

 1901, 'Purification of Washington water sup- 

 ply,' edited and compiled by Charles Moore, 

 Clerk of the Senate Committee on the Dis- 

 trict of Cohimbia. On page 195, a Commit- 

 tee of the Medical Society states that the most 

 important aspect "from which the two methods 

 of filtration shall be compared is in their rela- 

 tion to public health and more particiilarly 

 in relation to what they have accomplished in 

 the reduction of typhoid fever mortality in 

 cities where they have been employed. Viewed 

 from this standpoint, it appears that the me- 

 chanical filters, as first pointed out by Mr. 

 Hill, have accomplished relatively very little 

 in the reduction of typhoid fever .death rates. 

 In a subjoined table five American cities using 

 the mechanical devices are compared with five 

 cities in Europe using water from sand filters, 

 with an average for the year 1895 for the 

 American cities of 46.8 tjrphoid fever deaths 

 per 100,000 of the population against 6 deaths 

 per 100,000 for the foreign cities; that is to 



say, the American rate was almost eight times 

 as great as the foreign rate. Lest this com- 

 parison between foreign and domestic cities 

 be considered unfair, another table was pre- 

 sented showing the average number of deaths 

 from typhoid fever in several American cities 

 before and after filtration. This table shows 

 that while sand filters accomplish a reduction 

 of 78.5 per cent, in the number of deaths from 

 typhoid fever, the establishment and use of 

 mechanical filters have coincided with an in- 

 crease of 20.43 per cent., and even if the sta- 

 tistics from Elmira, Lexington and Newcastle, 

 where an increase was noted, are eliminated, 

 the reduction of typhoid fever in consequence 

 of mechanical filtration amounts to only 26 

 per cent., as compared with 78.5 by the process 

 of slow sand filtration. We believe that even 

 the more recent experiments at Pittsburgh 

 quoted by Sedgwick and Mason as indicative 

 of hygienic efiiciency of the mechanical filters, 

 show the inferiority of this system as com- 

 pared with the sand filter. 



EXPERIENCE OF SIX MONTHS AT PITTSBURGH, PA. 



If typhoid germs are proportioned to the 

 colonies of bacteria found in the effluent of a 

 filter, can any one deny that the prevalence 

 of typhoid fever among the users of each of 

 the three waters as deduced from the above 

 figures would be in the proportions of 105, 

 200 and 294, or nearly 1, 2 and 3, the advan- 

 tage being in favor of slow sand filtration? 

 From the testimony at hand there appears to 

 be no doubt that sand filtration has given bet- 

 ter results than mechanical filtration; the 

 former has been in use since 1839, and is an 

 imitation of natui-e, whose processes are gen- 

 erally simplicity and perfection, while the lat- 

 ter requires mechanical devices and is still 

 an experiment from the hygienic standpoint, 

 that is, as bearing on the prevalence of ty- 



