44 A PHYSICAL STUDY OF THE FIREFLY. 
In parenthesis it may be added that the light of the firefly did not produce 
fluorescence on the platinum barium cyanide screen, which is sensitive to 
X-rays. According to Mangold (1. c.) the older experiments, which indi- 
cated that fireflies emit X-rays, have long since been shown to be erroneous. 
In his recent experiments, Ives* also has investigated the question of phos- 
phorescence and the conclusion arrived at is that the light of the firefly has 
none of the properties of true phosphorescence. 
The oxidation theory has called forth more experiments than the theories 
just mentioned. ‘To this end the firefly has been subjected to all sorts of 
tests. For example, mechanical stimulation, such as percussion, pressure, 
etc., causes the quiescent, dark photogenic organs to burst into a glow. 
The application of heat or electric current causes the organs to glow. Ina 
vacuum the freshly excised quiescent luminous organs have been found by 
the writer to remain so, but on admitting air they glowed with great bril- 
liancy. The color of the light was the same as the ordinary glow in the 
living specimen. 
The experiments on the action of chemical stimuli are very numerous, no 
less than 68 different substances having been tried. ‘These substances 
include gases and vapors; also liquids and solutions of acids, alkalies, salts, 
and alkaloids. The most recent work along this line is by Kastle and 
McDermott,} whose paper should be consulted, not only for their own con- 
tributions, but also for their references (see appended Bibliography) to 
similar tests by earlier experimenters. These experiments show that cer- 
tain substances distinctly stimulate the light production; that others dis- 
tinctly inhibit the luminescence; and that still others have little or no effect 
on the light production. No definite relationship was found between chem- 
ical composition and the power to excite the living photogenic material to 
luminescence. The main point of interest is that anesthetics and related 
compounds act as a powerful stimulus to the light production. 
Probably the most important observation is the effect of water on the 
production of light by the photogenic material. As early as 1798 Carradori 
observed that the light emission is suspended by drying the photogenic 
organs and is revived again by softening in water. This phenomenon has 
been repeatedly verified by subsequent observers. Kastle and McDermott 
have kept the dry material in sealed glass tubes for 13 months (to Sept. 
9, I910; at the present writing almost two years have elapsed and the 
tests show that the photogenic material is still active), at the expiration of 
which time the specimens glowed actively for 15 minutes when moistened 
with water in the presence of oxygen. This moistening and redrying was 
repeated four times before the material ceased glowing.. Using hydrogen 
peroxide solution in place of water, the glow was more intense. 
In the conclusions to be drawn from the chemical aspect of the processes 
involved in the production of light by living organisms, three factors are 
required, viz, water, oxygen, and a substance to be oxidized. Just what the 
substance is that is oxidized is not known. Some have assumed it to be a 
fat, or an albuminous body. The histological study shows that the photo- 
*Ives, Phys. Rev., 31, p. 637, 1910. 
{Kastle and McDermott, Amer. Jour. Physiology, 27, p. 122, 1910. 
