LIGHT BY LIVING ORGANISMS—McDERMOTT. 3538 
Guanine appears to have been found in the reflecting layers of the 
photogenic organs of some marine forms, and Lund (’?) states that 
the dorsal layer in the firefly’s organ gives the test for guanine under 
some conditions. 
In summary 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 Watasé 
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 holdin 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 ("), 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 iquid, 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 may be 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°—smM 1911 23 
