160 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 heematoglobin, 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- 
