BEN T LEY GLASS 847 



reaction and the lluorcsccncc maxinunn ol ilic aniinoplulialaic ion is 

 to be found in water, but not in dimethyl suUate or other organic 

 solvents. 



H. H. SeHger has looked into some fmther aspects of the problem of 

 chemiluminescence by luminol. On the hypothesis that the emitting 

 species of molecide is the neutral luminol molecule, there woidd have 

 to be an energy transfer from some excited oxidation product to the 

 luminol molecule, and the quantum yield would be expected to de- 

 pend on the concentration of luminol. But experiment showed that 

 the quantum yield is constant for the concentration range from 10-'^ 

 M to 10-* M. Moreover, at the very pH where chemiluminescence 

 occurs, the fluorescence quantum yield of luminol drops practically 

 to zero. On the other hand, the chemiluminescence of luminol and 

 the fluorescence of the aminophthalic acid ion agree in spectrum al- 

 most exactly when both are measured at the same pH. The quantum 

 yield of the chemiluminescence decreases rapidly with increasing pH, 

 roughly parallel to the decrease in the fluorescence quantum yield of 

 aminophthalic acid above pH 11. Although the emitting molecule 

 is not yet positively identified, these findings clearly favor the hy- 

 pothesis that it is some excited oxidation product of the reaction 

 rather than luminol itself. 



Biolii7ninescence 



Since R. Dubois' classic demonstration in 1885 that the lumines- 

 cence of the firefly Pyrophnnis depends upon a reaction involving 

 separable heat-labile (protein) and heat-stable (non-protein) sub- 

 stances, similar "luciferase-luciferin" systems have been demonstrated 

 in widely separated branches of the animal kingdom, as well as in 

 certain bacteria, fungi, and dinoflagellates. Frank Johnson and his 

 collaborators have concisely surveyed these examples, which, having 

 evolved largely independently, show distinct differences in the bio- 

 chemical systems involved, and usually, except in closely related 

 species, manifest no cross-reactivity between the "hiciferin" of one 

 species and the "luciferase" of another. Examples of bioluminescence 

 occur in almost every animal phylum. In most of those studied, as 

 well as in the microorganisms and fungi, there is indirect, if not direct, 

 evidence of an enzyme-substrate system as the mechanism in the emis- 

 sion of light. Yet this is not to say that the systems are identical, 

 or even similar except in a general way. 



The three best-know^n systems at the present time are those of the 

 ostracod Cyridina, the North American fireflies Photinus and Photurus, 



