474 



Prof. H. Marshall Ward. 



[Dec. 14, 



FIG. 2. Plate similar to fig. 1, but exposed to the electric spectrum (obtained by 

 means of quartz apparatus) for twelve hours, and incubated four days. 

 The lower slot was covered with quartz only, the upper with a thin plate 

 of glass. The base-line in each case gives length of exposed slot. In both 

 cases the spores were uninjured in the infra-red, red (R), orange-yellow (Y) r 

 or green (Gr). The maximum effect was in the blue-violet, and it is interest- 

 ing to see how the bactericidal action extended far into the ultra-violet 

 (U V) in the case of the lower slot, where the light passed through quartz 

 only. The two little protuberances over UV were due to two little over- 

 flows of burnt Canada balsam at the edge of the slot, cutting off light. 



Some especially interesting results were obtained with the elec- 

 tric spectrum.* In the first place, the results with glass prisms, 



* The author records his thanks to his colleagues, Professor Stocker and 

 Mr. Shields, and to Drs. Woodhead and Cartwright Wood, for enabling him to try 

 a few preliminary exposures to the electric lantern last winter and spring ; these 

 yielded no results, however, and it was not until he was so fortunate as to secure- 

 the hearty cooperation of Professor Oliver Lodge that it was possible to accomplish 

 the photographing of the electric spectra in bacteria. To Professor Lodge and 

 Mr. E. Robinson the author takes this opportunity of expressing his special thanks 

 for the continuous pains they have taken to have his plates properly exposed. The- 



