This discovery was made by a Polish chemist, named Bronislaus Radziszewski, who followed it up with a long series of experiments on the phosphorescence of organic compounds, by which he was able to determine the conditions under which that phenomenon was exhibited.  In all the substances investigated by him in which phosphorescence was introduced he found that three conditions were essential to its production:  (1) that oxygen should be present; (2) that there should be an alkaline reaction in the phosphorescing mixture—­that is, a reaction such as is produced on acids and vegetable coloring matters by potash, soda, and the other alkalies; and (3) that some kind of chemical action should take place.

He found, moreover, that among the organic compounds that could be made to phosphoresce under these conditions were nearly all the fixed and ethereal oils.  With reference to the phosphorescence of animals, this observation is important, for it has been shown in a great many cases that a fatty substance forms the main constituent in their luminous organs.  This has long been known to be the case in the luminous insects belonging to the Lampyridae and Elateridae, as well as in the luminous centipedes; and the researches of Panceri, already referred to, on the luminous organs of many marine forms have shown that it holds good with regard to these also.

We may, therefore, conclude that substances fitted to phosphoresce under the conditions determined by the experiments of Radziszewski are generally, and probably universally, present in the luminous organs of phosphorescent animals.  Now, what is to be said as to the occurrence of these conditions?  The access of oxygen is in all cases easy to account for, but it must also be shown how the alkaline reaction is to be produced.  We need not expect to find in animal organisms potash, soda, ammonia, and the other common alkalies; but it was established by experiment that the alkaline organic compounds cholin and neurin, which are present in animal tissues, would also serve to bring about the phenomenon of phosphorescence in the substances on which the experiments were made.

Accordingly, it seems fair to conclude that when all these conditions for the production of phosphorescence in a chemical laboratory are present in animal organisms, the phenomenon, when observed in these, is exactly of the same nature as that which is produced artificially.  By that it is meant that animal phosphorescence is attended, like the artificial phenomenon, by a slow chemical action, or in other words, that the phosphorescent light is due to a gradual process of oxidation.

One curious circumstance has been discovered which lends still further probability to this explanation.  It was mentioned above that among phosphorescent plants there are several species of Agaricus.  Now, from one species of this genus, though not indeed one of the phosphorescent species (from A. muscarius) there has been extracted a principle called amanitia, which is found to be identical with cholin.  In the light of the results derived from the investigations just referred to it is reasonable to draw the conclusion that, if sought for, this principle would likewise be found in the phosphorescent species in which the other conditions of phosphorescence are also present.