EFFECT OF LIGHT 



21 



Table shoioing Elimination of Typhoid Germs in Agar 

 Plates on Exposure to Sunlight. 



With B. coli the results have been somewhat more variable, prob- 

 ably due to more changeable conditions. In one experiment, some- 

 thing over 80 per cent, of the germs were destroyed by fifteen 

 minutes' exposure, all being destroyed after four hours. The results 

 of this experiment were undoubtedly influenced greatly by clouds 

 in the sky, so that at times the sunlight was not very bright, after 

 about two and one-half hours the sun being entirely overcast. In 

 one experiment about 96 per cent, of the germs were ehminated at 

 the end of fifteen minutes, and after thirty minutes all of the germs 

 were destroyed. In these two experiments the water cultures were 

 exposed in plates, the results being shown in the following table : — 



Table showing Elimination of B. coli in Water Culttires on 

 Exposure to Sunlight. 



