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 Phyllirhoe bucephala, is also fully explained, ammonia being one of those alkaline substances which are so directly favorable to the exhibition of the phenomenon.

Nor is it difficult to account for the control which in some cases insects appear to have over the luminosity of the phosphorescent organs, exhibiting and withdrawing the light at will.  It is not necessary to suppose that this is an immediate effect, a conversion of nerve force into light, and a withdrawal of that force.  The action of the creature’s will may be merely in maintaining or destroying the conditions under which the light is manifested.  It may, for example, have the power of withdrawing the supply of oxygen, and this supposition receives some countenance from the observation cited from Kirby and Spence on the two captured glow-worms, one of which withdrew its light, while the other kept it shining, but while doing so had the posterior extremity of the abdomen in constant motion.  But the animal may also have the power in another way of affecting the chemical conditions of the phenomenon.  It may, for example, have the power of increasing or diminishing by some nervous influence the supply of the necessary alkaline ingredient.

But if animal phosphorescence is really due to a process of slow oxidation, there is one singular circumstance to be noted in connection with it.  Oxidation is a process that is normally accompanied by the development of heat.  Even where no light is produced an increase of temperature regularly takes place when substances are oxidized.  We ought, then, to expect such a rise of temperature when light is emitted by the phosphorescent organs of animals.  But the most careful observations have shown that nothing of the kind can be detected.  It was with a view to test this that Panceri dissected out the luminous organs of so many specimens of Pholas.  He selected this mollusk because it was so abundant in the neighborhood of Naples, where, his experiments were made; and in making his experiments he made use of a thermopile, an apparatus by which, with the aid of electricity, much smaller quantities of heat can be indicated than by means of the most delicate thermometer.  The organs remained luminous long after they were extracted, but no rise in temperature whatever could be found to accompany the luminosity.  Many experiments upon different animals were made with similar negative results by means of the thermometer.

The only explanation of this that can be given is probably to be found in the fact that the chemical process ascertained to go on in the phosphorescence of organic compounds on which experiments were made in the laboratory is an extremely slow one.