16 BACTERIOLOGICAL EXAMINATION OF WATER. 



At the commencement. 

 After four hours . 



At the commencement 



After two days 



At the commencement 



After three hours 



At the commencement 



After four hours . 



Exposed to light. Kept in the dark. Conditions. 



50,200 



9,600 



22,600 







3,328 

 



Buchner also arranged a series of experiments to determine 

 the effect of sunlight on cultures placed at different depths in 

 water. He prepared agar and gelatine capsules containing 

 B. typhosus, B. pyocyaneus and Sp. cholerae, and closed them 

 with india-rubber. On the upper surface of the capsules a dark 

 paper cross was fastened. The capsules were then placed in 

 water exposed to light with the following results : 



Distance of the plate 

 from the surface 

 of the water. 

 O'l metre. 

 1-1 .. 

 1-6 



CULTURE. 



Sp. cholerre. 

 B. pyocyaneus. 

 B. typhosus. 



DEVELOPMENT OF COLONIES. 



In the covered part 

 of the plate. 

 Very good. 



2-6 



3-1 



B. pyocyaneus. 



B. typhosus. 



Better growth 

 on the part 

 posed to light. 



{Slightly better than^j 

 the part exposed j- 

 to light. 



In the part exposed 



to light. 



Nil. 



Good. 



It appears therefore that in clear water the influence of light 

 on bacteria extends to a depth of two metres. 



Dieudonne worked with B. prodigiosus and B. fluorescens, and 

 showed that it was the light and not the heat rays which had a 

 destroying effect. The most powerful rays were the ultra-violet, 

 violet and blue rays ; the green rays had less power, and the 

 yellow and red rays appeared to have no action. Culture media 

 also appeared to be affected, hydrogen peroxide being developed 

 from the water present. 



Frankland and Ward investigated the influence of light on 



