114 THE POPULAR SCIENCE MONTHLY 
PHYSIOLOGIC LiGwt 
By F. ALEX. McDERMOTT 
HYGIENIC LABORATORY, U. S. PUBLIC HEALTH AND MARINE HOSPITAL SHRVICH 
ea are probably but few if any of the readers of this magazine 
who have not seen and admired at least one of the many mani- 
festations of “physiologic light,” of which the most common to us is 
the firefly. Indeed, from the earliest times the phenomenon of the 
emission of light by animals and plants has attracted man’s attention, 
and a large amount of scientific work has been done upon the subject. 
An attempt to compile a complete bibliography of the subject has 
resulted in the remarkable discovery that there are over seven hundred 
references to the literature bearing on the emission of light by organ- 
ized bodies, and “the end is not yet.” The work has embraced the 
physical, chemical, physiologic, histologic and entomologic sides, and 
much valuable information and many interesting facts have been se- 
cured. Among the names of the early writers who refer to some phase 
of this phenomenon are Aristotle, Pliny the Younger and Josephus; 
the more recent names include those of Robert Boyle, Sir Humphry 
Davy, Faraday, Pasteur, Kolliker, Dubois and the late 8. P. Langley, 
and indeed a host of others whose names are more or less widely known. 
Several extensive treatises on the subject have appeared, some of which 
are really quite good, though regrettably they are for the most part out 
of date at this time. For the benefit of those who may care to read 
further, the names of a few of these are given below.* 
The phenomenon of physiologic light has been variously termed 
“ phosphorescence,” “ luminosity,” “photogenic function,” etc., by dif- 
ferent authors. As these are, for the most part, interchangeable in 
meaning, they will be used in this paper to refer to the same thing. 
The term “ phosphorescence” is unfortunate, since it implies that the 
light is due to the presence of the element phosphorus—which it is not 
__and has become still more objectionable recently owing to its applica- 
tion by physicists and chemists to another totally different phenomenon 
of light emission. 
It was my good fortune during the summer of 1909 to be associated 
with Professor J. H. Kastle, of the University of Virginia (then chief 
1 Holder, C. F., “ Living Lights,” Scribner’s, 1886, New York; Gadeau de 
Kerville, “ Les Insectes Phosphorescents,” Rouen, 1881, 1887; Gadeau de Ker- 
ville, “Les Animaux et les Vegetaux Lumineux,” Paris, 1891 (German edition 
by Marshall, Berlin, 1893) ; Dubois, “Les Elaterides Lumineux,” Paris, 1886; 
Dubois, “Physiological Light,” Smithsonian Institution, Washington, D. C., 
Report for 1895, pp. 413-431. 
