EFFECT OF ULTRA-VIOLET RAYS. 



393 



the plate and the amoebas scraped from the agar^ thus forming a suspension 

 containing immense numbers of amoebae, both encysted and motile. A 

 little distilled water was then placed in a shallow dish, inoculated with 

 one large loopful of the suspension of amoebae, exposed to the rays and 

 immediately thereafter poured into a flask containing weak sterile bouillon. 

 After all inoculations and exposures had been completed the suspension 

 of amoebae was again examined microscopically and the presence of large 

 numbers of encysted amoebae demonstrated, thus proving that the encysted 

 forms had not changed into motile forms during the course of the 

 experiment. 



The flasks into which the exposed amoebae had been poured were 

 incubated for forty-eight hours and then examined foi- the presence of 

 the organisms. The results are shown in Table VI. 



Table VI. — Experiment 7: Clear loater inoculated with encysted amcebce, exposed 

 to ultra-violet rays, and the entire amount of loater poured into flasks of 

 bouillon; distance from lamp 10 centimeters. 



No. 



Time of exposure in seconds. 



Controls 



not 

 exposed. 



5 



10 



20 



30 



1 



2 





— 





— 



+ 



4 



5 





- 









1 



1 





This experiment conclusively proves that encysted amoebae are killed 

 by exposure to the ultra-violet rays for a period as short as five seconds. 



CONCLUSIONS. 



These experiments taken as a whole undoubtedly demonstrate that in 

 a water supply the amoebae, whether motile or encysted, may be killed 

 by a comparatively short exposure to ultra-violet rays. Balantidia, also, 

 appear to be destroyed by the same agency. These facts afford a very 

 potent argument in favor of the use of these radiations in the practical 

 sterilization of water in the Tropics. We have had no opportunity to 

 test the apparatus manufactured for this purpose, but since the results 

 of these preliminary experiments have proved so satisfactory we hope to 

 perform this important work in the near future with a view to de- 

 termining whether the rays are fatal to amoebae and other protozoal 

 parasites under the conditions obtaining with the commercial sterilizer 

 in practical use. 



106073 4 



