152 INFLUENCE OF PHYSICAL AGENTS. 



bacteria, and showed that by prolonged exposure to direct sunlight the 

 spores of various bacilli lose their capacity to germinate. About the 

 same time Arloing published his researches upon the influence of 

 light upon the development of anthrax spores. He found that the 

 anthrax bacillus was not restrained in its growth by diffused lamp- 

 light, but its growth was retarded by an intense gaslight. Spore 

 formation was more abundant in darkness than in red light, and more 

 abundant in red than in white light. When a screen was interposed 

 between the culture and the source of light, consisting of an aqueous 

 solution of hsematoglobin, the growth of the bacilli and of spores was 

 much more luxuriant than in white light. In yellow light it was less 

 abundant than in red. The blue and violet rays were still less favor- 

 able for the growth of the bacillus and the development of spores. 

 The pathogenic power of cultures was not especially influenced by 

 exposure to white gaslight. In subsequent experiments with sun- 

 light Arloing found that two hours of exposure to the July sun suf- 

 ficed to destroy the vitality of anthrax spores, but that a considerably 

 longer exposure (twenty-six to thirty hours) was necessary when the 

 spores had been allowed to germinate in a suitable culture medium. 

 Cultures which were not exposed long enough to destroy the vitality 

 of the bacilli were retarded in their growth, and subsequent exposure 

 for a shorter time (nine to ten hours) completely sterilized them. 

 Cultures which were weakened in their reproductive energy by ex- 

 posure to sunlight were also " attenuated " as to their pathogenic 

 power and could be used as a vaccine in protective inoculations. Ac- 

 cording to Arloing, the effect produced results from the action of the 

 full sunlight and cannot be obtained by the use of monochromatic 

 light. 



The experiments of Strauss seemed to give support to the view 

 advanced by Nocard that in Arloing's experiments spores did not 

 really exhibit a less degree of resisting power than the vegetating 

 bacilli, but that in fact they commenced to vegetate before they were 

 killed. Strauss placed anthrax spores in sterilized distilled water and 

 in bouillon, and found that, under the same conditions of exposure, 

 the bouillon cultures were sterilized in direct sunlight in nine 

 hours, while the spores suspended in distilled water grew when trans- 

 ferred to a suitable medium. This was accounted for on the suppo- 

 sition that the bouillon furnishes the necessary pabulum for the de- 

 velopment of the spores and that distilled water does not. 



Arloing combats this view and has published additional experi- 

 ments which seem to disprove it. He placed small flasks containing 

 anthrax spores in bouillon in the direct rays of the sun in February. 

 Some of the flasks were placed upon a block of ice which reduced the 

 temperature to 4 C. ; the others were not so placed, and the tempe- 



