1893.] 



Action of Light on Bacillus anthracis. 



23 



IV. " Further Experiments on the Action of Light on Bacillus 

 anthracis." By H. Marshall Ward, D.Sc, F.R.S., Pro- 

 fessor of Botany, Royal Indian Engineering College. 

 Received February 13, 1893. 



On December 15, 1892, I read to the Society a short account of 

 my experiments* proving that the light of a winter sun and that of 

 the electric arc rapidly destroy the life of the spores of the anthrax 

 bacillus, and showed that the bactericidal action is really direct, and 

 not due to elevation of temperature or to any indirect poisoning or 

 starving process incident on changes in the food materials. I also 

 mentioned that the evidence goes to prove that the effect is chiefly if 

 not entirely due to the rays of higher refrangibility in the blue- 

 violet of the spectrum. 



The experiments have been continued with special reference to 

 these latter points, and confirm the general conclusions in every 

 detail. Not only so, but the further results prove that the inhibitory 

 and deadly effects of direct insolation are not confined to Bacillus 

 anthracis, but also extend to other bacteria and even to the fungi; 

 and throw some light on several problems which have presented 

 themselves during previous investigations. 



Experiments with Screens of Coloured Glass. 



I will first describe seme experiments made during December to 

 February with coloured screens of various kinds ; premising that the 

 methods employed in preparing and exposing the plates, &c, have 

 been the same as those referred to in the previous communication. 



Ten pieces of glass of various colours were selected, and each care- 

 fully examined as to thickness, transparency, and spectroscopic pro- 

 perties, and labelled so that all notes could be readily compared and 

 contrasted. 



Perhaps the best method of presenting the comparative peculi- 

 arities of these glasses is that employed in the following table (p. 24). 



These pieces of glass were all of a size convenient for clamping 

 over the outside of the stencil plate put on to the Petri's dish, and in 

 which the letter or figure is cut (see p. 394 of previous paper). 



* See ' Roy. Soc. Proc.,' vol. 52, No. 318, p. 393. 



