392 



CHAMBERLAIN AND VEDDER. 



Table V. — Experiments 5 and 6: Results when clear and muddy loat&rs were 

 inoculated with amoebw, exposed to ultra-violet rays and the entire amount of 

 loater poured into flasks containing bouillon; distance from lamp, 10 centi- 

 meters. 



No. 



Experiment 5, 

 clear water. 



Experiment 6, 

 muddy water. 



Expo- 

 sure in 

 seconds. 



Culture 

 in flask. 



Expo- 

 sure in 

 seconds. 



Culture 

 in flask. 



1 

 2 

 3 



5 

 6 



10 

 10 

 20 

 20 

 30 

 30 



~ 



20 

 20 

 20 

 30 

 30 

 30 



— 



t 



Control 



notex- 



( posed. 



> + 



Control 

 ' not ex- 

 posed. 



' 



From Table V it is evident that amoebas were killed by the ultra-violet 

 rays in both clear and muddy water after ten-seconds' exposure in 

 the former ease and after twenty-seconds' in the latter. Another very 

 interesting and important point was noticed in experiment 6. The 

 control flask that received the Pasig Eiver water inoculated with amoebae 

 not only developed many amoebae after a few days' cultivation, but also 

 a large number of balantidia of unknown species. No balantidia were 

 found in any of the flasks containing water which had been exposed to 

 the ultra-violet rays. This affords very good evidence that balantidia 

 as well as amoebse are killed by ultra-violet rays. These balantidia are 

 more or less constantly present in the Manila water supply and are 

 probably harmless, but Balantidium coli is recognized as a dangerous 

 parasite. 



It will be remembered that in experiment 2 the encysted amoebae 

 on solid medium were not destroyed invariably by exposures of less than 

 forty seconds. In order to demonstrate conclusively that encysted amoebae 

 may be killed by short exposures to ultra-violet radiations the follow- 

 ing experiment was undertaken with a fluid medium, thus avoiding the 

 possibility that some organisms were protected from the rays by the 

 thick overlying film of amoebse and bacteria. 



Experiment 7. — Amoebse from the stock culture were grown on an agar 

 plate for forty-eight hours, at the end of which time microscopical exam- 

 ination showed very many encysted forms. These forms were as nu- 

 merous as the active organisms. A little distilled water was poured upon 



