Phosphorescence

The sponges, Alcyonaria, Bryozoa, mayflies, termites, spiders and Salpae contain reported luminous forms, whose light-produc tion is, however, doubtful. The light of many phosphorescent animals is not produced by the animals themselves but by sym biotic micro-organisms.

In general, luminous organs or regions are glandular and the luminous material may be ejected (extracellular luminescence) as a slime or a secretion, which in the squid, Heteroteuthis dispar, surrounds the animal in the sea water as does the black ink of other squids. Or the luminous material may be consumed within the photogenic cells (intracellular luminescence) as in the fire-fly and organisms possessing photophores. There is always a mechan ism for supplying the organ with abundant oxygen, a fact which indicates that the light-production is an oxidation.

Chemical Nature a Bioluminescence.—Knowledge of the chemical nature of bioluminescence has proceeded in four steps. ( I ) R. Boyle (1667) showed that fungi and bacteria required air (oxygen) for luminescence, becoming dark under an air pump and luminescing again when air was readmitted.

( 2)

Reaumur and Spallanzani (1794) showed that water was necessary, that luminous cells could be dried and preserved, in some cases indefinitely, producing light whenever moistened. This fact proves also that bioluminescence is not a process in volving definite structural peculiarities of the cell, as is the con traction of a muscle or the conduction of a nerve impulse, which will not occur after drying and moistening.

(3) Dubois, in 1887, found that the photogenic material could be separated into two constituents, luciferin and luciferase, due to marked difference in chemical behaviour. The latter is destroyed on boiling and behaves like an enzyme or catalyst; the former is heat-resisting and the oxidizable body. These substances can be treated like any other chemical compound, precipitated by certain reagents and redissolved in appropriate solvents. They have been partially purified but their chemical composition is still unknown.

Their isolation and synthesis is a matter of time and material.

(4) Harvey (1918) showed that luciferin, after oxidation to oxyluciferin, could be reduced again, that the luminescent pro cess was reversible and of the nature of an oxidative dehydro genation. It seems most probable that many organisms reduce the oxyluciferin formed during luminescence and thus re-utilize the material again and again, a principle that may in time be adopted in industry as the basis of an efficient method of illumination.

Bioluminescence is often spoken of as "cold light." This does not mean that no heat is produced, but only that very little ap pears as compared with the ordinary methods of illumination, which depend on the incandescence of carbon particle in flames or of wires through which a current is passing. The rise of tempera

ture in some luminous animals is less than o.00i° C. The light is no different, physically, from any other kind of light—it will affect a photographic plate, can induce chemical reactions, and can be polarized. There are no infra-red or ultra-violet radiations and no penetrating radiations are produced. Hence the luminous effi ciency, i.e., the percentage of the radiant energy which is visible, is very high, nearly 00%. This does not tell, however, what the radiant efficiency is, i.e., the percentage of the energy (chemical) of the oxidation process which appears as radiant energy; nor does it tell the overall efficiency, i.e., the energy (chemical) in the food of the animal which appears as visible radiant energy. This is the efficiency in which an illuminating engineer is interested, and studies on luminous bacteria have shown that the overall effi ciency of these forms is at least slightly and probably considerably greater than that of a nitrogen-filled incandescent lamp, when calculated from the energy of the coal necessary to run the dynamo that supplies current to the lamp.

The Uses of Luminescence.

Regarding the use of lumines cence to the animal, little can be said with certainty. In deep sea forms, living in perpetual darkness, it would seem that the organs must be lanterns for seeing or recognition, or for attracting prey. Many luminous forms live in light places, and it has been suggested that the luminescence may be a warning to scare away predacious animals which might molest the luminous forms, or a lure to attract creatures upon which the luminous animal feeds. These suggestions remain to be proven, but we do know that in the fire-fly the light acts as a signal or attraction to bring the sexes together. On the other hand, who can suggest the use of light to a luminous bacterium, an organism 26000 in. in diameter with no nervous reactions of a higher form, or the use to a pro tozoan, living at the surface of the sea, blown hither and thither by the wind? One is forced to the conclusion that in their case the light is merely fortuitous, a chance phenomenon, accompany ing some of the chemical changes in the organism.

It is well known that many substances produce light on slow oxidation (chemiluminescence) and the whole process of light production by luminous organisms can be so perfectly imitated by such reactions in the laboratory that we may no longer consider it a mysterious or unusual phenomenon.