38 A PHYSICAL STUDY OF THE FIREFLY. 
in the light, the solution obtained two years ago showing but little fluores- 
cence at the present time. 
After searching for some time for some one versed in the chemical side of 
the subject, who was sufficiently interested to investigate the chemical prop- 
erties of this material, Mr. F. A. McDermott has undertaken the subject 
and has recently published some of the results of his preliminary tests.* 
This fluorescent material is found in great abundance in Photinus pyralis, 
P. consanguineus, and P. scintillans. It is also present, in somewhat less 
abundance, in the non-luminous genus Ellychnia corrusca, a single speci- 
men of which is sufficient to show fluorescence in a small-sized tube contain- 
ing the alcoholic solution. Using the cadmium spark, there is no difficulty 
in observing the fluorescence. ‘The fluorescent material appears to be 
present in only a small amount in the Photuris pennsylvanica, and is not 
observable immediately after placing insects in a strong solution of alcohol 
and water. However, after standing a few hours, the fluorescence is visible, 
especially when excited by the cadmium spark. All previous tests for the 
fluorescent material in the various species made two years ago were verified 
this present summer. 
The rotary power of the solution of fluorescent material was tested by 
Messrs. Jackson and Snyder with an ordinary quartz-wedge saccharimeter. 
It was the extract of about 250 specimens of Photinus pyralis in 250 c.c. of 
water and alcohol. Using a 20 cm. column of the solution (after treating 
with lead acetate), the rotation was +0.04° Ventzke. The solution was 
then boiled to about one-fourth to one-fifth its original volume and filtered 
through four thicknesses of filter paper. The solution was a clear yellow, 
but on standing a precipitate was formed. ‘The rotation of a 20 cm. tube 
of the concentrated solution was 0.21° Ventzke. Using a 4o cm. tube, the 
rotation was twice this amount. Since 100° Ventzke=34.657° for the D 
lines of sodium, the actual rotation was 0.073° for the D lines of sodium. It 
wasconcluded that, since the concentration was evidently very weak as com- 
pared with an ordinary test solution of sugar, the natural rotary power of 
the solution containing the fluorescent material of the firefly was very high. 
The rotary power of this solution was again measured about five weeks 
later, the solution in the meantime having been kept in complete darkness. 
The small amount of precipitate present was removed just before examina- 
tion. ‘The observed rotation was 0.22° V., from which it appears that the 
rotary power of thesolution had changed but little, if at all, during this time. 
SUPPLEMENTARY NOTE. 
Since writing this paper, a recent note by Dubois (Compt. Rend., 153, p. 
208, 1911) has come to my notice in which he claims priority in the discovery 
of a fluorescent substance in animals, e. g., in Elaters and Lampyrids. He 
says he has gone a step farther than Ives and Coblentz, and McDermott, by 
defining its réle physiologically and by showing that “les insectes se servent 
naturellement, depuis bien des siécles sans doute, de l'emploi que l’homme 
vient seulement de faire industriellement de substances fluorescentes pour 
augumenter le rendement des appareils d’éclairage, en améliorant les quali- 
“McDermott, Jour. Amer, Chem. Soc., 33, p. 410, 1911. 
