EFFECT OF ULTRA-VIOLET RAYS. 



391 



to prove the presence of amoebse, the dish of water was then exposed to 

 the ultra-violet rays, and a second culture at once made to show the effect 

 of the exposure. The results of this experiment are shown in Table IV. 



Table IV. — Experiment J/.: Result of cultures from water inoculated with oMioebas. 

 Cultures made before and after exposure to ultra-violet rays; distance from 

 lamp, 10 centimeters. 



No. 



Culture 



before 



exposure. 



Exposure 



in 

 seconds. 



Culture 



after 

 exposure. 



1 



+ 



5 



— 



2 



+ 



5 



— 



3 



+ 



5 



— 



■ * 



+ 



5 



+ 



! 5 



+ 



10 



— 



6 



+ 



10 



- 



7 



+ 



10 



— 



8 



+ ■ 



10 



— 



9 



+ 



20 



— 



10 



+ 



20 



— 



11 



+ 



20 



— 



12 



a- 



•20 





13 



+ 



30 





14 



+ 



30 



— 



15 



+ 



30 



— 



16 



1 



+ 



30 



— 



This experiment was equally satisfactoiy in demonstrating that motile 

 amcebse can readily be killed by exposure to ultra-violet rays. In order 

 to clinch the matter two more experiments were perfoiTned. 



Experiment 5. — Distilled water was inoculated with amcebse, and ex- 

 posed in the same manner as in the previous experiment, but instead of 

 merely taking a loopful for cultivation after the exposure, the entire 

 amormt of water exposed was poured into a small flask containing bouillon, 

 and this flask was examined for amoebas after several days' cultivation. 



Experiment 6. — This was the same as the previous experiment except 

 that instead of distilled water, muddy water taken from the Pasig Eiver 

 was used. This was done in order to determine whether amoebae would 

 be killed in cloudy water or whether the rays would be intercepted by 

 the particles in suspension, thus permitting some amoebse to escape. 

 For controls in both of these experiments a dish of the water used was 

 inoculated and without exposure was at once poured into a flask of 

 bouillon. These two experiments are shown in Table V. 



