396 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 8 



rescence is only 0.015 percent (Adams, 1924). "If the efficiency of 

 other chemiluminescences proves to be as low as this, the commercial 

 significance of luminescence seems doubtful, to say the least. What 

 we really need in the case of luminous animals is a determination of the 

 heat of oxidation of luciferin together with the quantity of light pro- 

 duced per calorie, in order that the efficiency may be calculated" 

 (Harvey, 1924a). Now, the total efficiency of an acetylene flame is 

 about 17.7 percent; that of a sodium arc light about 60 percent; that 

 of a carbon filament about 4.54 percent (cf. Hodgman and Lange, 

 loc. cit.). To say that "an area of firefly light 6 feet in diameter on 

 the ceiling of a room 9 feet high would give ample illumination for 

 reading or drawing on a table 3 feet high" (Harvey, 1931c) is of in- 

 trinsic interest but is not adequate in convincing an illuminating 

 engineer who is interested in efficiency. In various circumstances, 

 however, a hot flame is not desirable and may be dangerous, while 

 luminescence would be harmless 



2. Intensity of the light. — The intensity of bioluminescence is 

 measured by a sensitive photoelectric cell and compared with that of a 

 standard lamp. In an in vitro suspension of luciferin-lucif erase, the 

 intensity of light varies directly with the concentration of the suspension 

 and with the temperature within limits (Qi °=ca. 2.74; Amberson, 

 1922). Even as little as one gram of the dry photogenic material of 

 Cypridina hilgendorfii will yield visible light when suspended in 

 1,700,000,000 gm (or cc) of water (Harvey, 1916a). The maximum 

 brightness of a prothoracic light organ of the intact firefly, Pyrophorus, 

 is 0.0002 candle at 20° C. (Harvey and Stevens, 1928). Coblentz 

 (1912) recorded an intensity variation for the firefly, Photinus pyralis, 

 varying between 0.020 and 0.0025 candle with the predominating 

 value at about 0.0025 candle. This insect will sometimes glow steadily 

 with a glow as low as 0.000020 candle in intensity (Harvey, 1919). 

 The average brightness of Photuris pennsylvanica is about 0.00067 

 candle (Parlin, 1935). During the Spanish- American war, Maj. Gen. 

 W. C. Gorgas, according to Parlin, "used the light from a bottle of 

 fireflies to carry out an operation." 



3. Wave lengths represented. — All light waves emitted by biolumines- 

 cence are, so far as known, within the range of the visible spectrum. 

 The light produced by the firefly, Photinus (Harvey, 1919), extends 

 only to the beginning of the blue, forming a band through the red to 

 the end of the green with a wave-length range of 6700 A. to 5100 A. 

 Other fireflies exhibit similar ranges (Pasteur, 1864; Young, 1870; 

 Langley and Very, 1890; Ives, 1910; Ramdas and Venkiteshwaran, 

 1931; Buck, 1937a, b). In the elaterid, Pyrophorus plagiophthalmus 

 (Buck, 1937b), the spectrum of the thoracic organ extends from 5075 A 

 to 6400 A.; that of the abdominal organ, from 5350 A. to 6400 A. 



