PHYSICAL NATURE OF ANIMAL LIGHT 45 



tral composition of the light emitted. Neither is it due, 

 at least in the fireflies examined, to the existence of color 

 screens which absorb certain rays, allowing only those 

 of a definite color to pass. The spectra of forms thus far 

 investigated are reproduced in Fig. 9 and recorded in 

 Table 5. It will be noted that they vary considerably 

 in position but are all of the same type. The spectrum 

 of Cypridina hilgendorfii is the longest thus far investi- 

 gated (A = .610/11 to A = .415ja), extending well into the 

 blue, and the light of this form is very blue in appearance. 



As first shown by Dubois (1886) for Pyrophorus, and 

 confirmed by myself for Cypridina, the light is not polar- 

 ized in any way. I may add that the Cypridina light like 

 any other light may be polarized by passing through a 

 Nicol prism. 



Several writers [Dubois (1914 book)], Fischer (1888), 

 Molisch (1904 book) have noticed that the light of lumi- 

 nous bacteria changes in color if grown on different culture 

 media. Light which is "silver white" on dead fish be- 

 comes ' ' greenish ' ' on salt-peptone-gelatin media and more 

 yellow on salt-poor media. Peron (1804) and Panceri 

 (1872) describe the light of Pyrosoma as yellow to green- 

 ish after death of the animal and reddish on stimulation ; 

 then fading out through orange, yellow, greenish and 

 azure blue. Polimanti (1911) describes the normal light 

 of Pyrosoma as greenish, and states that as the animals 

 die, or if they are kept at temperatures above the optimum, 

 the light becomes more red. McDermott (1911, b) noticed 

 that the light of fireflies placed in liquid air became deci- 

 dedly reddish just before going out and on rewarming the 

 first light to appear was reddish followed by the proper 

 shade at higher temperatures. I have frequently ob- 



