20 APPLIED BACTERIOLOGY 



ever, are those of Professor Marshall Ward, with the 

 very resistant and virulent spores of anthrax. Having 

 found that repeated exposure to sunlight destroyed the 

 spores in a few cubic centimetres of Thames water con- 

 taining a very large number, while a few weeks of bright 

 daylight greatly lessened them, he proceeded to make a 

 series of accurate experiments as follows : Agar plates of 

 anthrax were made in Petri dishes, using for this purpose 

 the virulent and resistant spores obtained by transferring 

 some of the material from an old culture into some sterile 

 distilled water, and keeping at a temperature of 56° C. for 

 twenty-four hours. The plates were then covered with a 

 metal stencil plate in which letters were cut, the dishes 

 stood on a black background, and then exposed to sun- 

 light for from two to six hours, after which the plates 

 were put into an incubator at 20° C. for forty-eight hours. 

 The agar was then found to be gray and cloudy, owing to 

 the development of an immense number of colonies, but 

 the space exposed to the light remained quite clear, show- 

 ing the form of the letters in the stencil plate. The same 

 results were obtained with other bacteria as well as with 

 fungi. Similar though less marked results were obtained 

 with an electric arc light, so much so that Professor Ward 

 thinks that this form of light may prove to be an effective 

 disinfecting agent. As with sunlight, however, its action 

 is necessarily confined to organisms directly exposed to the 

 rays, and not protected by media which absorb them, such 

 as even shallow water. 



Action of Coloured Lig:lit. — When a plate culture of 

 anthrax is exposed to the solar spectrum, the germicidal 

 action is found to be the strongest at the blue-violet end 

 (Ward). Janowski exposed cultures under screens of various 

 coloured glasses and aniline dyes, and found that no action 

 took place under brown or yellow; whereas solutions of 



