BASIS OF ANIMAL PHOSPHORESCENCE. 107 



If our organs concerned in the sensation of light were some- 

 what different from what they are now, it is possible that what 

 appears as luminous may have no such effect, and what appears 

 as dark may even appear as luminous. " It is quite conceivable 

 that animals might exist to which obscure heat rays might be 

 visible, and to which man and mammals generally would appear 

 constantly luminous." 1 



The animal organism is an actual apparatus of combustion, 

 in which carbon compounds are constantly burnt, and from 

 which carbonic acid is always escaping. There is no difficulty 

 in conceiving that organisms which produce heat in this way 

 may under certain circumstances produce light, if the combus- 

 tion of the material in the body could be carried on in such a 

 manner as to impart a more rapid vibration to the surrounding 

 ether than that which results in the production of thermal 

 radiation. 



The vibration of ether thus produced with higher frequency 

 and of shorter wave-lengths, such as we see in the fire-fly, 

 would affect the organ of vision, but not the organ of tempera- 

 ture. And this difference of result, so conspicuous to tis, may not 

 imply more than a very slight variation on the part of the indi- 

 vidual organism at the start. Nature desires, if I may use 

 such an expression, nothing but light in such an organism as 

 the fire-fly, and produces this with the least possible waste. 



That this is a legitimate inference may be shown from the 

 several works of physicists. Several years ago Professor 

 Young 2 examined the spectrum of the fire-fly and stated his 

 important observations in the following form. 



" The spectrum given by the light of the commom fire-fly of 

 New Hampshire (Photinus f) is perfectly continuous, without 

 trace of lines either bright or dark. It extends from a little 

 above Fraunhofer's line C in the scarlet to about F in the 

 blue, gradually fading at the extremities. It is noticeable 

 that precisely this portion of the spectrum is composed of rays, 

 which, while they more powerfully than any others affect the 



1 Mosely: Notes by a Naturalist on H. M. S. Challenger, 1892, p. 512. 



2 C. A. Young : Spectrum of the Fire-fly. Amer. Naturalist, Vol. Ill, 1870, 

 p- 615. 



