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. consanguine us, and P. scintilla us. 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 0.2 1 Ventzke. Using a 40 cm. tube, the 

 rotation was twice this amount. Since ioo Ventzke = 34.657 for the D 

 lines of sodium, the actual rotation was 0.073 for the D lines of sodium. It 

 was concluded 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 the solution 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, 19 1 1 ) 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 role physiologically and by showing that "les insectes se servent 

 naturellement, depuis bien des siecles sans doute, de l'emploi que fhomme 

 vient seulement de faire industriellement de substances fluorescentes pour 

 augumenter le rendement des appareils d'eclairage, en ameliorant les quali- 



*McDermott, Jour. Amer. Chem. Soc, 33, p. 410, 191 1. 



