ACTION OF LIGHT ON MICRO-ORGANISMS 361 



colonies made their appearance, whilst that portion of 

 the culture material which the sun's rays had reached 

 through the cut-out letters was sterile, or nearly so. 

 Buchner's paper is accompanied by a drawing copied 

 from a photograph representing such a circular dish in 

 which the cut-out letters formed the word c TYPHUS/ 

 and the sharpness of their contour is remarkably strik- 



FIG. 22. TYPHOID BACILLI IN AGAR-AGAR, EXPOSED TO DIRECT 



SUNSHINE FOR ONE HOUR. 



(After Buchner.) 



ing. In order to obtain such sharp photobacteriographs, 

 as we propose to call them, Buchner points out that 

 the culture material must be thickly sown with the par- 

 ticular bacteria, so that the resulting colonies shall 



