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 Pflüger 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.