352 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
McDermott (°°) has recently recorded the results of some experi- 
ments with liquid air, which show that exposure of the photogenic 
tissue, fresh or desiccated, to this temperature, and grinding while so 
exposed does not in the least affect the ability of the substance to 
produce light upon restoration to the normal temperature. Macfad- 
yen (**) found that, while exposure of the luminous bacteria to the 
temperature of liquid air did not inhibit their ability to produce 
growth and light upon return to the normal conditions, trituration 
at this temperature permanently destroyed the photogenicity. It 
would appear, then, that there is some essential difference between 
the microorganism and the insect in this regard. 
The photogenic bacteria present many interesting problems; their 
ability to grow and luminesce in a medium consisting only of a solu- 
tion of 3 per cent of sodium chloride and 1 per cent of asparagin in 
water; the dependence of the marine species on the presence of certain 
mineral salts, and these in certain concentrations, and upon the pres- 
ence of oxygen, for light production; the pathogenic and symbiotic 
relations existing between some species of these photobacteria and 
some higher organisms are all matters of great interest. McDer- 
mott (*°) made some experiments with the view of determining any 
chemical resemblances that might exist between these bacteria and 
the fireflies. The work was on the whole inconclusive, but indicated 
that if proper conditions could be arranged liquid cultures of the 
bacteria might be dried and afterwards caused to produce light on 
moistening. Molisch (*) found that the thicker layers of growth of 
photobacteria on solid media could be dried and would exhibit their 
photogenic activity on moistening. 
The well-known work of Radziszewski (°°) has already been referred 
to, and also the more recent researches of Trautz (*). Delépine (*) 
has experimented with a large series of thiocarbonic esters and 
related bodies, which appear to be ‘‘ phosphorescent”’ as the result of 
oxidation, a phenomenon to which this writer has given the name 
‘“‘Oxyluminescence.”’ Hernandez and Cerdan (*) have questioned 
Delépine’s view of the nature of the ‘‘phosphorescence” in these 
cases, and refer it to a form of triboluminescence. In any event, 
work along this line has some bearing on the problems of biophoto- 
genesis, and it seems not too much to expect that it may develop that 
in organic chemistry there will be found to be “photophore” or 
‘‘nhotogen’”’ groupings, just as we now have chromophore and fluoro- 
phore groupings, fluorogens, etc. . 
Various observers have found the urates and phosphates of ammo- 
nium, sodium, potassium, and calcium in the luminous tissue and its 
ash. Dubois at one time seems to have rejected the oxidation theory 
and to have believed that the light was due to the spontaneous 
crystallization of ammonium urate (crystallo luminescence). 
