MICROBIOLOGY OF SEWAGE 339 



generality can be extended to sewage is debatable. Our best informa- 

 tion leads to the belief that any reduction in numbers of typhoid 

 bacteria which may take place within the sewer before discharge is of 

 minor importance and of slight sanitary significance. 



Discussion of other pathogens must be in even more general terms. 

 Information is almost wholly lacking and it can only be assumed for 

 purposes of safety that, in so far as organisms of these various types are 

 discharged into the sewer, they will persist to a certain extent in the 

 sewage until it is finally disposed of. If such disposal be by discharge 

 into a stream without purification, then the waters of that stream 

 become polluted with infectious material. Studies recently made by 

 Sedgwick and McNutt have indicated the possibility that many dis- 

 eases, other than the oft-quoted typhoid fever, may be transmitted 

 in this way. 



Life in Septic Tanks and Filters. With the introduction of the 

 septic tank at Exeter, England, in 1893, the question of the fate of 

 pathogenic bacteria in such a tank was raised. It was even suggested 

 that bacteria, such as the typhoid organism, might multiply in the 

 tank. The question was investigated by Professor Sims Woodhead, 

 who concluded that no organisms capable of setting up morbid changes 

 in animals were discharged from the tank. This negative evidence, 

 however, has little weight in the light of more recent experiments. 

 Pickard introduced an emulsion of typhoid bacteria into this same tank 

 and noted only a gradual decrease. After fourteen days he was able 

 to detect i per cent of the initial number. He also reported a removal 

 of 90 per cent of the typhoid organisms introduced into a contact 

 filter. These data must be interpreted in the light of two established 

 facts. The typhoid organism tends to die at a rapid but diminishing 

 rate under any but the most favorable conditions. This results in a 

 rapid decrease at first, with a prolonged survival of a few individuals. 

 This process takes place in sewers, in streams, and, in fact, under most 

 artificial conditions. The second fact of importance is the difficulty 

 of recovering the typhoid organism under experimental conditions like 

 those described. 



A thorough study of the bacteriology of sewage and of filter effluents 

 led Houston to conclude that the biological processes at work in a filter 

 or tank were not strongly inimical, if hostile at all, to the vitality of 

 pathogenic germs. 



