A series of experiments was carried out for the purpose of determining whether the reaction of rabbits inoculated with Treponema pallidum might be influenced by their light environment. The conditions compared were (1) diffuse sunlight filtered through window glass and subject to variations due to natural causes, (2) constant and continuous exposure to artificial light with a wave-length of from 3022 to 5790 Ångström units (Cooper Hewitt), and (3) complete exclusion of light.

The results showed clearly that each of these conditions produced a distinctive effect and that the effect tended to conform to the nature of the environmental condition. In general, the efficiency of the reaction to infection increased with the amount of light received and with the constancy of the exposure.

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