LIGHT BY LIVING ORGANISMS — McDERMOTT. 353 



Guanine appears to have been found in the reflecting layers of the 

 photogenic organs of some marine forms, and Lund ( 42 ) states that 

 the dorsal layer in the firefly's organ gives the test for guanine under 

 some conditions. 



In summaiy it may be said that the biophotogenic process is prob- 

 ably an oxidation in all cases, and that the substances whose oxidation 

 produces light is a complex product of cell metabolism containing 

 both fatty and albuminous radicals, and probably differing in com- 

 position in each type of organism. The mechanism of the process 

 may vary — the oxidation may be direct or indirect — according to the 

 type of photogenic organ and the particular species of organism in 

 point. 



Light is a form of energy, just as are heat, electricity and chemical 

 affinity. We know that in many chemical reactions a great deal of 

 the energy of chemical affinity is transformed, probably directly, into 

 heat, and sometimes some of it appears as electricity. If sufficient 

 heat is generated, a portion of the original chemical energy may be 

 transformed into light indirectly through the agency of the heat, the 

 phenomenon being known as incandescence. But there appears to 

 be no good reason why some of the chemical energy might not appear 

 directly as light if the conditions are favorable, and indeed it is quite 

 evident that such is sometimes the case, unless we adopt the view of 

 the "combustion of food particles in the tissues," referred to Watase 

 a little while ago. For instance, the light-producing reaction 

 between hydrogen peroxide and an alkaline solution containing 

 pyrogallol and formaldehyde, generates considerable heat, enough to 

 make the container uncomfortable to hold in the hand, yet nothing 

 approaching that required for incandescence, and it is certainly incon- 

 ceivable that there could be particles heated to incandescence by 

 chemical action in a solution. It seems possible, however, that in the 

 lecture experiment described by Schwersenski and Caro ( 61 ), in which 

 it appears that alcohol is oxidized by ozone in the presence of the 

 powerful dehydrating agent sulphuric acid, there may actually be 

 small explosions, with incandescent temperatures, in the liquid, though 

 it is not impossible that the flashes of light observed result from the 

 direct transformation of chemical into radiant energy. If, in the 

 pyrogallic acid reaction, solid sodium peroxide be used instead of 

 alkaline hydrogen peroxide, a flame maybe produced, but the charac- 

 teristic light in the solution is produced at the same time, and it 

 seems probable that the flame is due to the combustion of the vapor 

 of formaldehyde (driven off by the heat of the reaction) in the oxygen- 

 rich atmosphere produced by the evolution of oxygen during the 

 solution of the sodium peroxide. It is of some interest in connection 

 with Radziszewski's work, that in both this reaction and that of 

 Schwersenski and Caro the active substance may be an aldehyde. 

 38734°— sm 1911 23 



