LUMINOSITY OF ANIMALS (Alt,.
lumiL:ositoS, splendor, from Lat. luminosus, from tuturn, light. from merry, to shine; connect ed with Gk. Xelucbs, leukos, white, Skt. rue, to shine, ()Church Slay. tuella, moon, Orr. 14chc, lightning. 0111 . huh/. Ger. Licht, AS. lr.oht, Eng. light). The property possessed by many ani mals of giving oil from the whole or purl of their surface a light similar in appearance to that of phosphorescence. This light was at first supposed by many to be in smite way due to the presence of phosphorus in the animal*, tissue, and hence the name phosphorescence MIS first given to this kind of luminosity. Subsequent in vestigation has made it certain that phosphorus has nothing whatever to do with the phenomenon. This kind of light continues or is emitted only in the presence of oxygen. Fabre demonstrated that the luminous mushroom ( Agariens) gives more carbonic-acid gas while luminescent than at other times, and Max Schultze has called attention to the fact that the photogenic cells of the light ning bug are always found in close relation .with the traehe:e. if these photogenic cells are placed near perosmie acid they draw oxygen front the acid. Nadziszewski has studied the conditions under which chemical substances exhibit luminescence and has found that a whole series of substances emit light when they are permitted to combine with oxygen in an alkaline solution. Such sub stances are fats, ethereal oils, hydreca•b. and alcohols, but heat is necessary with some of them for the production of light. Since in living tis sue fats, oils, and the like are present. tog, ther with substances which give an alkaline reaction, the that arc essential for are present. Wielowiej-ki and. Emerrt conclude that the photogenic stabstat ces exist in the cells of the luminous organs. and may be in tlo na ture of fats. while Dubois, from his studies on Pyrophorus, C011siders the light to be due to two substances, •luei fern se' and 'Inciferine.' Luci ferase he believes to be in tl e nature of an elIZVIlle which exists in the fi run I minute grail The seeollil exists in the blood and becomes luminous only when it is borne into the Imninous organ. believes the photo genic material to he the product of secretion of the cell, formed as the result of metabolism in the cell, and in the process of its formation iden tical with that known as secretion. Ile says fur
ther that the process of secretion does not neces sarily imply the existence of a gland; the funda mental process of secretion may be carried. out by an isolated single cell just as well as by thou sands of similarly constituted gland-cells. For the luminous apparatus of deep-sea fishes, see and the accompanying plates.
The emission of light by living substances is widespread. It is an especially significant fact that. of the wonderful pelagic animals whose delicate transparent bodies occupy the upper strata of the sea and float about as plankton, al most. all possess luminous power. Associated with this fact is the presumption that the lumi nous capacity of living substances is possibly much wider spread than is realized, that we do not see the light because the organisms are not trans parent, or because the production is too feeble to allow the light to be seen through thick body layers; indeed, it is not impossible that in our own bodies certain cells may be photogenic. In most cases, as in Minimills insects. Verworn says, the power of emitting light is a peculiarity spe cially perfected by selection, and possesses its own significance for the life of the animals in question. In pelagic marine animals, also, such a significance is certainly present ; as a rule, these animals emit light suddenly and only upon stimu lation, and hence it may lie supposed that the light serves as a means of frightening enemies.
Luminescence is a phenomenon common both to animals and plants. Thus certain bacteria that live in sea-water, or those of putrefaction. such as Buct cri phosphoresecn 8, Which lives on dead flesh, cause luminescence. At least two kinds of these bacteria are known to prod nee a blue light, and one a greenish light. It is easy to make artificial cultures of these forms so as to study their growth and activities. Certain mushrooms of the genus Agariens, which grow upon wood cud ea use its decomposition, are also hunineseent. The blossoms of nasturtium, mari gold. poppy, and other plants. and even the leaves, have been observed to emit light occa sionally. Possibly the light in the latter cases is of electrical nature.