Annals of the Transvaal Museum. 
62 
the caustic alkalies could be replaced by ckolin, neurin, and other 
substances found in living creatures. The light from these carbon 
compounds was shown by the spectroscope to be identical in nature 
with that produced by photogenic organisms. Watose had previously 
stated that the light of the fire-fly was the result of oxidation in 
alkaline media of a granular secretion of the photogenic cells. 
The only opposing voice is that of Dr. Raphael Dubois. He 
wholly discards the oxidation theory and substitutes for it that of 
a reaction between two substances which he claims to have isolated 
and to which he has given the names luciferose and luciferine. He 
admits that oxygen and moisture are essential to the reaction. He 
states, however, that in his experiments, the effect of oxygen was to 
extinguish the light without first giving any increase in brilliancy. 
As a large part of Dubois’ experiments were upon a marine 
mollusc, it seemed that a comparative study of the light of Photinus 
with that of some marine organism would be helpful. Consequently 
I followed the work previously done with the fire-fly by a summer 
at the Marine Biological Laboratory at Wood’s Hall, Massachusetts. 
The form chosen was Mnemiopsis leidyi. The work done was very 
far from complete, but even so it seems significant. 
Mnemiopsis leidyi , one of the Ctenophores, is quite common near 
Wood’s Hall during the summer months. It is a beautiful jelly-fish, 
almost as transparent as the sea water. The specimens upon which 
I worked varied from one to six inches in length. The light is 
produced by cells lying between the longitudinal rows of swimming 
plates. It is given only when the Ctenophore is disturbed in some 
way. 
When the living animal is placed in various solutions and gases 
the effect seems to depend almost entirely upon the extent to which 
it is irritated. The same agents give entirely different results when 
the photogenic tissue is brought directly under their influence. When 
live Ctenophores are placed in acid and alkaline solutions they flash 
more frequently in the former, but very soon die in both. When the 
photogenic tissue itself is placed in acid solutions, the light is wholly 
extinguished and does not reappear under the influence of oxygen. 
In alkaline solutions the light persists for a considerable time and 
becomes more brilliant when oxygen is passed over the tissue. 
Material left for half an hour in an acid became luminescent when an 
excess of alkali was added, and gave a brilliant light under the 
influence of oxygen. 
There remains a wide field for investigation. There are very 
great differences in structure between fire-flies of closely related 
genera, and little has yet been done with the multitude of marine 
light-givers. I believe, however, that in all forms, however widely 
separated, we shall find the process of photogeny to be essentially the 
same and to be one of oxidation. 
