1892.] On the Action of Light on Bacillus anthracis. 393 



ing the loose subcutaneous tissue in the form of a well-defined curved 

 band, with the convexity generally directed forwards, it reaches and 

 becomes continuous with the periosteum surrounding the distal ex- 

 tremity of the ungual phalanx. These two structures, viz., the ungual 

 corium and the periosteum of the ungual phalanx, which are histo- 

 logically very similar to one another, and distinct from the connective 

 tissue forming the bulk of the terminal segment of the digit, are thus 

 placed in complete continuity by means of the curved band of dense 

 connective tissue above described. 



V. " Experiments on the Action of Light on Bacillus anthracis." 

 By H. MARSHALL WARD, F.R.S., Professor of Botany, Royal 

 Indian Engineering College. Received December 15, 18i)2. 



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 authorwent further into this particular question 

 with results 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 sun-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, and that 

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

 reduces the number of spores capable of development on gelatine, 

 it seemed worth while to try the effect of direct insolation on plate- 

 cultures, to see if the results could be got more quickly and 

 defmitely.t 



Preliminary trials with gelatine plate-cultures at the end of the 



* See p. 237 of " First Report to the Water Research Committee of the Royal 

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

 1891. 



t It appears that Buclmer (' Centr. f. Bakt.,' vol. 12, 1892) has already done this 

 for typhoid, and finds the direct rays of the summer sun quite effective. 



