EFFECT OF ULTRA-VIOLET RAYS. 



387 



cuiated. Part of these plates were inoculated with a loopful from the 

 stock culture of amcebse, part from a stock culture of Bacillus typhosus, 

 and part from a stock culture of Bacillus dysenterice. A few of the plates 

 inoculated with each organism were at once placed in the incubator to 

 serve as controls while the remainder were exposed to the rays as described 

 above, for periods varying from five to eighty seconds, and after the 

 exposure they also were placed in the incubator. In order to compare 

 the effects of the rays at different distances from their source, exposures 

 were made at point 10, 15, and 23 centimeters from the lamp. After 

 incubation for twenty-four hours, the plates were examined for growth 

 and the results of this experiment are contained in Table I. In this as 

 in subsequent tables, the plus sign means that growth occurred, while the 

 ininus sign indicates a sterile plate or culture. 



Table I. — Experiment 1: Agar plates exposed to ultra-violet rays immediately 

 after inoculation, and then incubated 24 hours. 



The figures in parentheses in the 5-second column Indicate the number of colonies 

 found on the plate after incubation. 



As is shown clearly in Table I, a profuse growth was found on all 

 of the controls which were not exposed to the rays. Of the plates 

 exposed for five seconds at 10 and 15 centimeters, some of those in- 

 oculated with bacteria showed growtli and others were sterile, but none 



