XI, B, 2 



Gabel: Examinations of Swimming Pools 



71 



was thought advisable to determine the variations in bacterial 

 count between the water collected in the morning and that col- 

 lected in the afternoon. 



Table B. — Comparison of morning and afternoon bacterial content of 



swimming pools, 



[Numbers indicate colonies per cubic centimeter of water.] 



Sample taken — 



Aug. 31 at 8 a. m __ 

 Aug. 31 at 3 p. m __ 

 Sept. 4 at 7. 30 a. m 

 Sept. 4 at 4. 10 p. m 



Pool I. 



Plain 

 agar. 



2.000 



4,000 



100 



3.600 



Litmus 



lactose 



agar. 



2,500 



10, 000 



4,300 



200 



Congo 

 red 

 agar. 



1,400 

 1,800 

 2.100 

 1,900 



Aver- 

 age. 



2,000 

 5.300 

 2,200 

 1,900 



Pool II. 



Plain 

 agar. 



4,800 



40,000 



600 



4,200 



Litmus 



lactose 



agar. 



4,700 



23, 000 



3,500 



4,100 



Congo 

 red 

 agar. 



3,300 



13, 000 



4,100 



2,200 



Aver- 

 age. 



4,300 



25, 600 



2,700 



3,500 



From the data in Table B it is seen that the bacterial count 

 in the afternoon is usually higher than early in the morning, 

 when the water has not been stirred up so much by swimmers. 

 The average forenoon count for pools I and II was 2,800 and the 

 average afternoon count was 9,050. For pool III the difference 

 was even greater, the forenoon count being 2,300 and the after- 

 noon count averaging 66,700. A study of the attendance at 

 these pools showed that neither the weekly nor daily variations 

 were sufficiently great seriously to interfere with our work and 

 results. The daily general average of attendance was 32. 



The average counts of the three pools on all samples taken 

 before September 20 are given here to exemplify the variations 

 due to different media at the temperatures used. 



Average counts on samples from three pools. 



Plain nutrient agar, 25° C. 

 Litmus lactose agar, 37° C. 

 Congo red agar, 37° C. 



Average number 

 of colonies. 

 9,500 



9,100 



11,600 



The average counts of all samples taken after September 20 

 on plain agar are 462,290 for 25°C. and 587,445 for 37°C. 

 incubation, the former being about 88 per cent of the latter. 



In a number of instances, after samples had been removed for 

 bacteriological tests, a few cubic centimeters of bouillon were 

 added to the bottle of water in order to promote the multiplication 

 of protozoa which might be present. These specimens were 

 examined microscopically, after three days' storage at room 

 temperature. 



