20 APPLIED BACTERIOLOGY 



In the experiments of Momont (1892), dry anthrax spores 

 were found to resist the action of light for a long time, but 

 moist spores freely exposed to the air failed to grow after 

 forty-four hours' exposure to sunlight. In the absence of 

 spores, anthrax bacilli in a moist condition freely exposed 

 to the air failed to grow after from half an hour to two 

 hoiirs' exposure to sunlight; but in the absence of air 

 these same bacilli were not destroyed at the end of fifty 

 hours of exposure. Buchner found that broth cultures of 

 typhoid, Bacillus coli communis, Bacillus pyocyaneus, and 

 the Vibrio cholercs Asiaticce yielded no growth after one 

 hour's exposure to direct sunlight. 



The most recent and conclusive experiments of all, how- 

 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 



