LIGHT BY LIVING ORGANISMS McDERMOTT. 347 



marine forms, e. g., the Cephalopoda and the Pennatulidse, give lights 

 of several colors. Among the insects the only forms known definitely 

 to present wide differences from this general similarity are the trop- 

 ical species of Phengodes as observed by Barber ( 2 ) and others, which 

 possess a photogenic organ, located back of the head, that gives a dis- 

 tinctly reddish light. No spectroscopic studies of this red light of 

 Phengodes have been made. Coblentz ( 5a > 6 ) has given spectrographic 

 proof of the differences in the color of the lights of Photinus pyrdlis, 

 P. consanguineus, and Photuris pennsylvanica, attention having been 

 called to the physiologic differences by the author ( 46 ) and others, 

 [Knab ( 36 ), Turner ( 68 )]. The author has recently had an opportunity 

 to examine the light of Phengodes laticollis (female) with the pocket 

 spectroscope referred to in his paper in the Canadian Entomologist, 

 1910 ( 46 ), and found it to consist mainly of a narrow band in the 

 yellow-green and green, with very much fainter ends stretching toward 

 the red and blue ; the definite ends of the band could not be made out 

 on account of the feebleness of the light, and the predo min ance of 

 the greenish band may, of course, be mainly due to the greater 

 retinal sensitiveness to these tones. 



Forsyth ( 21 ) has claimed that cultures of certain photobacteria give 

 spectrophotographic evidence of the existence of ultra-violet rays in 

 then* emitted light. It seems to the author that this observation is 

 in need of confirmation, not that it is impossible, of course, but that 

 it is at variance with previous work and with present ideas of the 

 properties of physiologic light. McDermott ( 49 ) failed to find evi- 

 dence of ultra-violet radiation in the light from cultures of Pseudo- 

 monas lucifera Molisch, and, as would be expected, also failed to find 

 any indication of appreciable radioactivity. 



It need scarcely be said that the light of the firefly affects the pho- 

 tographic plate; obviously spectrophotographic studies could not 

 otherwise have been made upon it. Photographs have been taken 

 by means of the light of the photogenic bacteria and of the cucuyo. 



In 1896 Muraoka ( 54 ) announced that he had proved the penetra- 

 tion of metal films by means of the light of the firefly in a manner 

 similar to that of the X-rays. The author has failed to find any evi- 

 dence of the penetration of thin sheet copper, aluminum foil, or the 

 black paper with which X-ray plates are wrapped by the light of 

 Photinus pyralis. It seems that under certain circumstances sub- 

 stances which do not actually emit penetrating radiations may affect 

 the photographic plate, and an explanation of Muraoka's results has 

 been offered by Molisch ( 52a ' 5S ) based upon bacterial or vapor influ- 

 ence; but when we consider that his results were published only a 

 little while after the discovery of the X-ray it seems possible that 

 Muraoka was just a little over-enthusiastic. However, Singh and 



