XI. B, 2 Gabel: Examinations of Swimming Pools 65 



tained public natatoria, their cost ^ having probably hindered 

 their establishment in larger numbers. Pools maintained by 

 educational institutions have been examined more carefully than 

 the majority of public pools, since the facilities for bacterio- 

 logical work were near at hand.' 



The occasional established instances of public-bath infections, 

 together with exaggerated popular accounts of acquired sores, 

 ear troubles, venereal diseases, etc., alleged to be due to infec- 

 tion from contaminated swimming tanks, have caused many to 

 look with aversion upon water that has been in contact with 

 other persons. Since contagious diseases are more prevalent 

 in the tropics than in temperate regions, it is especially im- 

 portant that in countries like the Philippine Islands every pos- 

 sible precaution be taken to prevent the dissemination of 

 infectious material through the medium of bath waters. Much 

 more work has been done on the purification of sewage and of 

 drinking water than of bath water, but fortunately the results 

 of the work on the former are in a great measure applicable to 

 the latter. 



Both physical and chemical methods of purification have been 

 employed in attempts to render such waters innocuous. Among 

 the physical methods that have been used to purify water 

 bacteriologically are heat, ultra-violet light, and filtration. 

 These methods have generally been considered too costly for 

 swimming pools. The last gives good results and is used to 

 some extent, but not nearly as much as for drinking water. 

 Heating water to from 60° to 70°C. has been found ' to give 

 adequate purification. 



Many chemical methods have been devised for purifying 

 water. Certain of these methods, through the coagulation of 

 colloids and the formation of precipitates, lessen the turbidity 

 of the water, causing it to appear fresher and cleaner. The 

 use of such substances as mineral acids, alkalies, potassium 

 permanganate, corrosive sublimate, sodium benzoate, boric acid, 

 and ozone has been recommended, but most of them have 

 proved to be too expensive for general use or otherwise im- 



• Report of the President of the Borough of Manhattan, New York 

 City (1912). 



'Bunker, J. W. M., Science (1910), n. s. 31, 556; Ravenel, Am. Phy. 

 Ed. Rev. (1912), 17, 684; Manheimer, W. A., Pub. Health Rep. (1915), 

 30, 2796. 



' Dunbar, W. P., Leitfaden f. d. Abwasserreinigungsfrage. R. Olden- 

 bourg, Berlin (1907), 341. 



