Report on the Bacteriology of Water. 303 



otate oi water. 



Number 

 of drops 

 used. 



JN umber ot 

 antiirax per 1 c.c. 

 original. 



Ivemarks. 





1 



270,000 







1 



153,000 









117,000 







1 



140,000 









130,000 







3 



135,000 





Here, again, we abstain from dwelling too much on the quantitative 

 resnlts, though, so far as they go, they suggest that aeration favours 

 the sporification or preservation of the anthrax, while insolation — 

 even feeble — tends to destroy the spores. But the positive qualitative 

 result is obvious, that the anthrax if it passes over into the spore 

 stage in these waters becomes, thereby, to a great extent removed 

 from the direct competition with the water organisms. 



Experiments on the Action of Light on Bacillus anthracis. 



It is abundantly evinced by experiments that direct insolation 

 in some way leads to the destruction of spores of Bacillus anthracis, 

 and in so far the results merely confirm what had already been dis- 

 covered by Downes and Blunt in 1877 and 1878.* 



From the fact that an apparent retardation of the development of 

 the colonies on plates exposed to light was observed several times 

 under circumstances which suggested a direct inhibitory action of even 

 ordinary day-light, the author went further into this particular question 

 with resnlts as startling as they are important, for if the explanation 

 given of the phenomena observed in the following experiments turns 

 out to be the correct one, we stand face to face with the fact that by 

 far the most potent factor in the purification of the air and rivers of 

 bacteria is the sun-light. The fact that direct snn-light is efficacious 

 as a bactericide has been long suspected, but put forward very vaguely 

 in most cases. 



Starting from the observation that a test-tube, or small flask, con- 

 taining a few c.c. of Thames water with many hundreds of thousands 

 of anthrax spores in it may be entirely rid of living spores by con- 

 tinued exposure daily for a few days to the light of the sun, first 

 shown for water by Straus (' Soc. de Biologie,' 1886, p. 473), and that 

 even a few weeks of bright summer day-light — not direct insolation 

 — reduces the number of spores capable of development on gelatine, 



* See p. 237 of " First Keport to the Water Kesearch Committee of the Koyal 

 Society" (' Roy. Soc. Proc.,' vol. 51, 1892) for the literature on this subject up to 

 1891. 



