The Nature of Animal Light

Excerpt

CHAPTER I
LIGHT-PRODUCING ORGANISMS

The fact that animals can produce light must have been recognized from the earliest times in countries where fireflies and glowworms abound, but it is only since the perfection of the microscope that the phosphorescence of the sea, the light of damp wood and of dead fish and flesh has been proved to be due to living organisms. Aristotle mentions the light of dead fish and flesh and both Aristotle and Pliny that of damp wood. Robert Boyle in 1667 made many experiments to show that the light from all three sources, as well as that of the glowworm, is dependent upon a plentiful supply of air and drew an interesting comparison between the light of shining wood and that of a glowing coal. Boyle had no means of finding out the true cause of the light and early views of its nature were indeed fantastic. Even as late as 1800 Hulme concludes from his experiments on phosphorescent fish that the light is a "constituent principle of marine fishes" and the "first that escapes after the death of the fish." It was only in 1830 that Michaelis suspected the light of dead fish to be the result of some living thing and in 1854 Heller gave the name Sarcina noctiluca to the suspected organism. In 1875 Pfluger showed that nutrient media could be inoculated with small amounts of luminous fish and that these would increase in size, like bacterial colonies, and we now know that the light of all dead fish and flesh is due to luminous bacteria.

In the early part of the nineteenth century it was surmised that the light of damp wood was connected with fungus growth because of a similarity in smell. In 1854 Heller recognized minute strands, which he called Rhizomorpha noctiluca, as the actual source of the light. We now know that all phosphorescent wood is due to the mycelium of various kinds of fungi and that sometimes the fruiting body of the fungus also produces light.

The phosphorescence or "burning of the sea," which is described by so many of the older explorers, is also due entirely to living organisms, both microscopic and macroscopic. The latter are mostly jelly-fish (medus?) or comb jellies (Ctenophores) and give rise to the larger, more brilliant flashes of light often seen in the wake or about the sides of a steamer at night. The former are various species of dinoflagellates or cystoflagellates such as Noctiluca (just visible to the naked eye) which collect at the surface of the sea and often increase in such numbers that the water is colored by day (usually pink or red) and shines like a sheet of fire when disturbed at night. Although Noctiluca was recognized as a luminous animal in 1753 by Baker, the light of the sea was a mysterious phenomenon to the older observers. MacCartney, speaking before the Royal Society in 1810, outlines the various older theories as follows: "Many writers have ascribed the light of the sea to other causes than luminous animals. Martin supposed it to be occasioned by putrefaction; Silberschlag believed it to be phosphoric; Prof. J. Mayer conjectured that the surface of the sea imbibed light, which it afterwards discharged. Bajon and Gentil thought the light of the sea was electric, because it was excited by friction.... I shall not trespass on the time of the Society to refute the above speculations; their authors have left them unsupported by either arguments or experiments, and they are inconsistent with all ascertained facts upon the subject. The remarkable property of emitting light during life is only met amongst animals of the four last classes of modern naturalists, viz., mollusca, insects, worms, and zoophytes." MacCartney recognized the true cause of the light, although he had little idea of the vast number of marine forms which are luminous and omits entirely any reference to the fishes, many of which produce a light of their own when living, apart from any bacterial infection.

A survey of the animal kingdom discloses at least 36 orders containing one or more forms known to produce light and several more orders containing species whose luminosity is doubtful. In the plant kingdom there are two groups containing luminous forms. The distribution of luminous organisms is brought out in the . Those orders are printed in italics which contain species whose self-luminosity is fairly well established. It will be noted that further subdivisions into orders is not given in classes of animals which lack luminous forms.