34 THE NATURE OF ANIMAL LIGHT 



luminescence and triboluminescence of AsClg and of 

 K0SO4. By photographing- the luminescence through color 

 screens of different absorptive power (Weiser, 1918, a) 

 a spectrum of the light could be obtained, and it was 

 found to be identical in both the tribo- and crystallo- 

 luminescent light; in the case of AsClg, a band in the 

 green-blue, blue and violet. Weiser believes the light 

 in this case also to come from recombination of the ions, 

 As""^^ + 3C1~ = AsCl.}, and that crystalloluminescence in 

 general is due to rapid reformation of molecules from 

 ions broken up by electrolytic dissociation while tribolu- 

 minescence is due to rapid reformation of molecules from 

 ions broken up by violent disruption of the crystal. Of 

 course in triboluminescent organic crystals which do not 

 dissociate into ions, some other reaction must be respon- 

 sible for the light. One thing seems certain, that the two 

 types of luminescence are similar. As Bigelow * remarks, 

 ^^It is altogether probable that the cause of this (crystal- 

 loluminescence) *Svhatever it may be, is the same as the 

 cause of triboluminescence, whatever that may be. ' ' 



Crystals are not found in the luminous organs of ani- 

 mals with the exception of the fireflies. In these a layer of 

 cells occurs (see Chapter IV) filled with minute crystals 

 of one of the purine bodies (xanthin or uric acid). One 

 might surmise that the light of the animal was a cr^^stallo- 

 luminescence accompanying the formation of these crys- 

 tals. It is easy to show, however, that the light comes 

 not from the crystal layer but from another layer of cells 

 containing large granules. It is also dependent on the 

 presence of oxygen while crystalloluminescence takes 

 place in the absence of oxygen. The crystal layer possi- 



. Theoretical and Physical Chemistry, 1912, p. 516. 



