ri, 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.

On this theory of the production of the phenomenon now under
consideration, the effect of shaking or of vital action in giving rise
to or intensifying the exhibition of the light is accounted for by the
fact that by these means fresh supplies of oxygen are brought into
contact with the phosphorescent substance. The effect of ammonia on
the light emitted by the sea-slug _Phyll