1892.] 



Action of Light on Bacillus anthracis. 



395 



eight hours at 20 C., and on removing tlie wrappers the colonies of 

 anthrax were found densely covering all parts of the plate except the 

 area a letter or cross, &c. exposed to the sun-light. There, how- 

 ever, the spores were killed, and the agar remained perfectly clear, 

 showing the form of a sharp transparent letter, cross, &c., in a ground- 

 work rendered cloudy and opaque by the innumerable colonies of 

 anthrax. 



Experiments proved that this was not due to high temperature, for 

 a thermometer with its bulb next the irisolated glass rarely rose 

 beyond 14 to 16 C., and never beyond 18 C., and even if the 

 thermometer did not record the temperature inside the plate, this 

 can scarcely have been much higher. 



As long as this latter point remained uncertain, however, the 

 experiments could not be regarded as satisfactory; whence it was 

 necessary to again have recourse to gelatine cultures. The gelatine 

 employed began to ran at 29 C., and in November it was found that 

 such plates exposed outside, either to directly incident sunshine, or 

 to directly reflected rays, showed a temperature of 12 to 13 C. at the 

 insolated glass surface, and even five to six hours' exposure caused no 

 running of the gelatine. 



FIG. 1. 



