We are, therefore, constrained to conclude that this subject is still open for elucidation by future inquirers. If it should be proved that some of the higher animals really do emit light from their eyes, independently of the in cidence and reflexion of that from without, it will go far to render it probable that, in lumi nous animals generally, the development of light depends more upon the movements of some imponderable agent in and from their nervous system, than upon the nature of the composition of the fluids poured out by the luminous organs.
Another series of phenomena, intimately connected with, and illustrative of, those previ ously considered, demands notice here, namely, the shining of fishes, and other animal bodies shortly after death. The luminousness of dead fishes is a very common subject of observation, but not on that account the less worthy of par ticular attention. It has been ascertained that the light is given out from every part of the body, external and internal, that is exposed to the air ; and that on the surface of the luminous parts there is a slight moisture, or solution of the tissues of the animal, which can be scraped off; or diffused in water, and Continues lumi nous for a short time after being so removed. When pieces of the skin or muscle of a fish are placed in a little water, the luminousness appears only on the surface when the water is at rest; but whenever it is agitated the light is diffused through the whole body of ivater.
In some fishes, as the whiting, this lumi nousness appears within a very short time after death ; in others, not for some days ; but in all it ceases before the truly putrefactive process has commenced. It is observed that those fishes which most quickly putrefy, are also those which give out light the soonest.
From the circumstance mentioned above, that this luminous fluid formed on the bodies of dead fishes is miscible with water, and re tains its luminousness for a short time after being so mixed, it has been concluded that the beautiful phenomenon of the phosphorescence of the sea may be frequently owing to the pre sence, in great quantity, of the remains of fishes recently dead. It is certain that the mast
careful observers sometimes fail to detect any entire living animals in sea water taken up from a brilliantly luminous sea ; and find only abundance of small fibres and shreds of what seem to be broken-down animal tissues. Pro fessor Smith* concluded from his own obser vations made in the Atlantic, that, while the bright sparkling light of the surface of the ocean is always emitted by living animals, that duller diffused luminousness, which is fre quently seen over a vast extent of the sea, giving it the appearance of milk, is given out by " a dissolved slimy matter, which spreads its light like that proceeding from phosphorus." Under the most powerful microscope, Smith saw nothing in such water but "the most mi nute glittering particles, having the appearance of solid spherules." Humboldt saw a great extent of the surface of the sea rendered almost gelatinous by the admixture of numbers of dead dogysa and medusa.
It may, therefore, be regarded as probable, at least, that the luminousness of the ocean is sometimes caused by dead matter; but it is certain that, in the great majority of instances, it is entirely owing to the presence of living animals, possessed of the light-giving property:l in attempting to examine these, so as to deter mine their forms and habits, it is important to keep in mind that they are sometimes ex tremely small, so as to be distinguished with considerable difficulty, even with the aid of the best microscopes. And when they are larger, they are frequently so transparent as to elude notice.