596 



PRINCIPLES OF GENERAL PHYSIOLOGY 



and Very, 1904). Fig. 183 gives photographs of the spectrum of the light 

 of the fire-fly, taken by Coblentz. It will be seen that the spectrum extends 

 considerably less, both towards the red and towards the violet, than that 

 of the carbon filament lamp. It is, in fact, according to Coblentz, very like 

 that of an ideal radiator at a temperature of 5,000. Langley and Very (1890) 

 showed that the heat radiation of Pyrophorus noctilucus (a South American 

 beetle) is only one-four-hundredth of that given out by incandescent source^, 

 such as candle light, reduced to the same luminosity. 



In its chemical aspect, the phenomenon is evidently an oxidation. In many 

 cases, the cessation of light in absence of oxygen and its reappearance on 

 admission of oxygen have been demonstrated. The nature of the substance 



A 



FIG. 183. LIGHT OF FIRE-FLY COMPARED WITH THAT OF ARTIFICIAL SOURCES. 



A, Photographs of spectrum of carbon {flow-lamp, for different exposures. 



B, Photographed spectra of 



1, helium vacuum tube. 3, 5, and 6, fire-fly, Photinwi pyralix 



2, carbon glow-lamp, four watts per candle power. | 4 and 7, fire-fly, Photinus pennxylvanica. 



The colours of the bright lines in the spectrum at the" top are as follows : 



447 M, blue. -471 C-, bluish green. -5015 M, green. '5876 M, yellow. -6678 M, reddish orange. 7065 M, red. 



jfote that the light emitted by the fire-fly is confined to the middle region of the spectrum and is most intense 

 in the yellow-green, while that of the carbon glow-lamp is most intense in the orange (see the uppermost spectrum 

 in A, below the bright line comparison spectrum). (Coblentz, 1912 ) 



(Carnegie Institution of Washington.) 



oxidised is not yet known. The particular case of Pholas has been referred 

 to above (page 362). According to Dubois (1913), the oxidation here is under the 

 control of an enzyme, an " oxidase " ; the secretion is luminous after removal 

 from the cells, as can readily be verified. In any case, the reaction seems to 

 be independent of the "vital" activity of cells. Schultze (1864) finds a 

 substance which reduces osmic acid in the luminous organs of the glow-worm, 

 probably a derivative of oleic acid. 



There is evidence that a certain small amount of heat is developed in the 

 active glands of the fire-fly (Coblentz, 1912, p. 33), but this appears to be 

 associated with the secretory process. 



Water is necessary. Dried material can, however, be brought to shine again 

 by moistening. 



Although the production^ of light can occur by reaction with oxygen of 



