XI. B. 2 Gabel: Examinations of Swimming Pools 83 



bacterial content, no uniform relation between the two could be 

 established. 



SUMMARY AND CONCLUSIONS 



Experiments have been made on three pools of 200 to 225 

 cubic meters' capacity, supplied with city water, which is a 

 chlorinated river water with a temperature of about 28° C, The 

 one hundred eighty-nine samples of 50 cubic centimeters of 

 water were obtained about 1 meter below the surface and plated 

 about forty minutes later on agar. After incubating at 25° 

 and 37°C. for twenty-four hours, counts were made, and the 

 positive presumptive tests for B. coli were further tested by 

 plating. 



Congo red lactose agar gave good results, but Endo medium 

 seemed preferable for the confirmatory tests for B. coli. In the 

 fermentation tubes lactose bile without peptone did not give 

 as good results as lactose neutral red bouillon or lactose bouillon. 

 One and 10 cubic centimeters of the water were inoculated, the 

 latter into 30 cubic centimeters of the medium. Bacillus coli 

 was found in the swimming pools to be usually not much more 

 abundant than is accepted as permissible in drinking water. It 

 was reduced most effectively by adding once a week 2 parts of 

 copper sulphate per million parts of water. One week the daily 

 addition of 0.5 part chlorine as calcium hypochlorite per million 

 parts of water gave better results, while during another week 

 the results were not as good as when the copper sulphate was 

 used. 



Copper sulphate produced a greater turbidity than calcium 

 hypochlorite. An increase of disinfectant caused an increase in 

 turbidity. Conversely, from the condition we find in a suspen- 

 sion of bacteria in water, due to the addition of a disinfectant, 

 the number of bacteria often varied inversely as the turbidity, 

 but not invariably. Consequently the determination of the 

 turbidity would not be a practical test for determining the 

 pollution in these pools. This can best be shown by regular 

 tests for B. coli and the number of other bacteria present. 



When a swimming pool is merely emptied and refilled, the 

 bacterial count of the fresh water is much higher than when the 

 emptied pool is thoroughly cleaned before refilling. 



An increased amount of a given disinfectant invariably reduced 

 the average numbers of B. coli and the total bacterial counts, 

 as is graphically shown in fig. 1. This curve also shows the 

 relation of the counts at 37 °C. and those at 25° C, the former 

 amounting to 116 per cent of the latter. 



