PHYSICAL NATURE OF ANIMAL LIGHT 49 



per sec), while the tungsten lamp gives one mean spheri- 

 cal candle for 1.6 watts, about one-third the energy, and 

 the latter is consequently more efficient. 



As we know practically nothing of the energy trans- 

 formations occurring during the process of light produc- 

 tion in organisms, all statements regarding the efficiency 

 of their light are based on relations between the visible 

 radiation and total radiation. This involves a measure- 

 ment of rays in the infra-red region (heat rays) and ultra- 

 violet region (actinic rays) as well as the light rays 

 proper, and any other radiant energy produced. While 

 all spectroscopic investigations show that the spectrum of 

 luminous animals never extends to the limits of the visible 

 spectrum in either the red or violet, it is possible that 

 bands occur in the infra-red or ultra-violet, and special 

 methods must be employed to detect these. Radiations of 

 all kinds, if converted into heat on striking the blackened 

 surface of a thermopile, bolometer, or radiometer can be 

 measured by changes in temperature and the relative 

 amounts of energy represented be compared in a common 

 unit, the calorie. By proper screening, all rays except the 

 visible light rays can be cut off from the measuring instru- 

 ment and the amounts of energy represented in light and 

 in total radiation thus be determined. 



Dubois (1886) first studied this problem in Pyrophorus 

 by the use of a thermopile and galvanometer and foun^d 

 a small amount of radiation from the luminous region in 

 excess of that from a non-luminous region. It amounted 

 to a galvanometer deflection of 0.95° and was increased 

 0.3° during the flash of the insect on electrical stimulation. 

 This increase of 0.3° is possibly due to heat produced on 

 muscular contraction. In any case the amount of heat 



