The investigation of the pollution and sani tary conditions of the Potomac watershed under the supervision of the United States Hygienic laboratory reported in Bulletin No. 104 dis closed 20 or more genera of living organisms, including bacilli con communes in great quan oties Spore-forming anerrobia, gas producing organisms, were found in parts of the river ollpolhsted by sewage, thus proving that those Irrmg ornisms may be found in any surface waters. The biology of rivers has been treated by Dr. S. A. Forbes, Prof. It F.. Richardson and others in this country and by Dr. A. C. Houston in his 'Report on Research for The Metropolitan Water Board of London' and by W. G. Savage of England. The American Pub lic Health Association in its report on (Stand ard Methods of Water Analysis' in 1912, sug tested tests to discover bacteria in water. Typhoid fever and other deadly diseases may have their inception from the bacteria in such unwholesome waters. It is, therefore, of vital importance to all communities, that they be provided with pure water supplies. This may accomplished- by treating such waters in a esanrier to rid them of bacteria and all other foreign organisms. Other bacteria will be mentioned under the several processes for their elimination.
The general acceptance of 'the germ theory of disease' led to investigation into the media of transmission of pathogenic microbes. Pot able water was found not only to be a pur srior of such bacteria but a medium for their propagation. The epidemic of Asiatic cholera in Europe in 1847 and in 1850 has since been attributed largely to contaminated water sup plies. The British Parliament, suspecting that such might be the case, in 1852 passed its first act requtri the filtration of the Metropolitan Water Supply. Later Dr. Robert Koch actually discovered the cholera bacillus (B. enact-es .iriarice or comma bacillus) and found that it would exist for some time in water. Ile thereby demonstrated that cholera might be spread through water supply of communities, as it ap peared to have been spread during the epidemic of 1847 and 1850, Upon the surface of an open sand filter at Boston six genera and four and one-third million organisms were found in one itmare centimeter of sand. All were not patho renic but some are an aid to filtration. How ever when the decomposition of such organisms in water sets in, it may impart offensive odors. These have been grouped as aromatic, grassy and fishy, thereby indicating the genus under going decomposition and disclosing the char acter of pollution.
The most numerous and prevalent patho genic microbes found in American and foreign surface waters are the typhoid bacilli, which caused a death rate of 23.3 per 100,000 popula
tion in 48 cities of the United States in 1910. That is four times the death rate per 100,000 population in Berlin, Vienna and London from typhoid fever per annum. But the death rate from typhoid in America is being lowered, as greater efforts are being made to secure pure waters for municipal and general potable pur poses. Fortunately for rural populations most of their supplies are from ground waters, which are free or largely so from bacteria, except where such ground waters are near enough the surface to be polluted.
Dr. Koch discovered a method of eliminat ing bacteria from surface waters, which was to allow the water to percolate through slow filters. Those were found to remove most of the microbes from the water as it percolated through such layers of sand and grave! A single filter, however, did not always arrest all the living organisms in the water, so that two or three sand filters came into use. The filter beds at first are not wholl impervious to the transmission of bacteria. t was learned from experiments that the surface must first be coated with a film of mud and microbes before the latter were entirely arrested. When such a film is completely formed over the surface of the layer of sand, then the filter efficient and may be kept in operation as long as water continues to percolate through it. Then its layers may be washed by drawing off the water standing in the basin and by forcing filtered water up through the layers of sand and of coagulated matter. While the filtered water is being so forced up through the layers, they and the coagulated matter thereon may be agitated by raking as is done in the works of Pittsburgh, or they may be agitated by mechanical devices. In this manner the coagulated matter is lifted and freed from the surface of the sand. Filtra tion may then be resumed. This may be repeated once or twice before it is necessary to scrape off the coagulated matter and the upper layer of sand to the depth of one or two inches, which is all that is necessary to remove, in order to dispose of the pathogenic microbes and other foreign bodies and the mud and silt. The layers of sand so removed may then be cleansed, dried and replaced in the filter basin and filtration may be resumed. There are various methods of renovating sedimentary and infiltration basins, but the foregoing methods illustrate some of the processes in general use. It is a well-known fact that bacteria propagate rapidly and there is always a possibility that some may pass through a filter and con taminate the water that has passed through such filter.