INFLUENCE OF PHYSICAL A(,KNTs. 161 



rature. in the open air where all were exposed, was 11 C. All of the 

 spores failed to grow after an exposure of four hours. When exposed 

 in water the time of exposure was longer. 



Roux has shown that the light also has an effect upon the culture 

 medium, and that sterilized bouillon which has been exposed to direct 

 sunlight for some hours restrains the development of anthrax spores 

 subsequently introduced into it, but not of the growing bacilli. His 

 experiments show that access of oxygen is a necessary factor in the 

 sterilization of cultures by sunlight. 



In the experiments of Moment (ISO'-?) 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' ex- 

 posure to sunlight. In the absence of spores, anthrax bacilli in a 

 moist condition, when freely exposed to the air, failed to grow after 

 exposure to sunlight for half an hour to two hours ; but in the ab- 

 sence of air the same bacilli were not destroyed at the end of fifty 

 hours' exposure. 



Geisler (1892), in experiments made upon the typhoid bacillus, 

 found that all portions of the solar spectrum except the red rays ex- 

 ercised a restraining influence upon the development of this bacillus. 

 The electric light gave a similar result. The most decided effect was 

 produced by rays from the violet end of the spectrum. The restrain- 

 ing influence appears, from the researches of Geisler, not to be due 

 solely to the direct action of light upon the development of the 

 bacilli, but also to changes induced in the gelatin culture medium 

 employed in his experiments. 



In his address before the International Medical Congress of Berlin, 

 1800, Koch states that the tubercle bacillus is killed by the action of 

 direct sunlight in a time varying from a few minutes to several hours, 

 depending upon the thickness of the layer exposed. Diffused day- 

 light also has the same effect, although a considerably longer time of 

 exposure is required when placed close to a window, from five to 

 seven days. 



Dieudonne (1804), in experiments upon Bacillus prod igiosus and 

 Bacillus fluorescens putidus, found that direct sunlight in March, 

 July, and August killed these bacilli in one and one-half hours, in 

 November in two and one-half hours. Diffuse daylight in March 

 and July restrained development after three and one-half hours' ex- 

 posure (in November four and one-half hours), and completely de- 

 stroyed vitality in from five to six hours. 



Ward's experiments (180-2-1804) show that the blue and violet 

 rays have decided germicidal power, while the rays at the red end of 

 the spectrum are comparatively inert. This corresponds with results 

 previously reported by Arloing. 

 11 



