ii4 THE POPULAR SCIENCE MONTHLY 



PHYSIOLOGIC LIGHT 



By F. ALEX. McDERMOTT 



HYGIENIC LABORATORY, U. S. PUBLIC HEALTH AND MARINE HOSPITAL SERVICE 



THERE 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 Eobert Boyle, Sir Humphry 

 Davy, Faraday, Pasteur, Kolliker, Dubois and the late S. 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. 1 



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, 18S6, 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. 



