saline watery fluid into which the medusa almost entirely melts when removed from the water. This viscid liquid produces itching when applied to the skin, as does also the juice of several non-luminous medusæ. The luminous matter may be scraped off-renders bodies smeared with it phosphorescent-and when mixed with water, urine, and particularly with milk, forms mixtures which remain luminous for several hours-are increased in brightness by agitation or by warming to 37° C.-may be again. rendered luminous after their phosphorescence has ceased-but when strongly heated, are deprived of their luminosity for ever. (Luminous fluids of this kind may also be obtained by mashing up the entire animal in water; if sea-water is used for the purpose, the mixture shines but feebly.) The medusa shines in water like a torch, so brightly that it can be seen at the distance of 100 paces. Its light is most brilliant when the alternate contraction and enlargement of the disc succeed each other with the greatest rapidity; the light is also strengthened by motion from withWith the diminution of this oscillation the light becomes fainter, and when it ceases, there remains only a very faint luminosity, which may also be observed after death, and does not disappear till putrefaction sets in; it is likewise increased for a time by rubbing. A medusa which has died out of water, and is no longer luminous but beginning to deliquesce, recovers its luminosity in fresh, but not in sea water: the water also becomes luminous. (Spallanzani.)

out.

The luminosity of Medusa lucida in water is increased by warming, till the water becomes so hot as to kill the animal. In alcohol it shines still more brightly, but soon dies and ceases to be luminous. Placed in water under an exhausted receiver, it shines as strongly as under the ordinary pressure of the air. The electric spark seems to have no action upon it; electric shocks cause the light to disappear for an instant, but it immediately reappears with increased brightness. (Macartney.)

In Aurelia, the light proceeds from the base of the tentacula; in Beroë from the vessels under the laced filaments. (Edw. Forbes.)

If a Physalia be immersed in alcohol it instantly ceases to shine, because it dies.-Zoophytes do not shine when at rest, but only after exertion, and consequently increased respiration, inasmuch as locomotion and respiration are with these animals one and the same movement. Their light becomes fainter as their vital force diminishes, and ceases with their death. This takes place after often repeated exertion and luminosity thence resulting. (Tilesius.)

In the Pennatula phosphorea, the light proceeds, not from the stem, but only from the feather, and is excited only by motion, either spontaneous or induced from without. After death, luminosity is produced by touching the animal, a luminous slime being at the same time expressed from the feather. (Spallanzani.)

In Alcyonum exos, likewise, the phosphorescence exists not in the stem, but in the individual polypi. (Leuckardt.)

The phosphorescence of the sea at night-which sometimes diffuses a universal but dull glimmer of light, sometimes presents a fiery surface, at other times shines only in places where it is set in motion by ships or oars, at others again exhibits single sparks, stars, balls, chains, or bands of fire-is mainly attributable to small luminous animals which inhabit the sea. The separate luminous spots are produced by the larger Medusa, Salpæ, and Pyrosomæ, which emit the most vivid light. (Tilesius.) The general luminosity of the sea is produced by various animals, but more especially by small crustacea whose light is of a sparkling character, by

Nereids, and great numbers of small Meduse. When sea-water of this nature is filtered, the luminous matter remains on the filter. (Sparmann, Tilesius.) Water taken out of the brightly-shining sea near Martinique gave no light when at rest; on blowing upon it, small bodies crossed the liquid in all directions, shining the brighter the more strongly the surface was blown upon. When stirred, the water became luminous throughout: on being warmed to 35° C. it also became brightly phosphorescent; but when further heated to 43°, its luminosity was completely destroyed. Hydrochloric, sulphuric, and nitric acid, ammonia, carbonate of potash, and alcohol likewise produced a sudden and generally evanescent light. The water after passing through a filter could no longer be rendered luminous: there remained on the filter a number of small animals discernible by the microscope, and consisting of a globule having a yellow spot and a tail, which they moved with great rapidity. (Artaud.)-Moreover, the phosphorescence of the sea is probably often produced by the luminous putrefaction of marine animals, by insolation (as appears to be the case from an experiment of Hellwig), and by electricity, as supposed by Rivière, Le Gentil, and Bajon.

Instances have been known of men whose perspiration is adhesive and phosphorescent, so that the phosphorescence is communicated to their linen; the smell of this perspiration, in the case of an individual of gouty diathesis, in whom the perspiration broke out after violent dancing, was urinous and sour (Henkel, Crell. N. Chem. Archiv. 2, 291); in another it had a peculiar phosphoric odour. (Hermstadt, Magaz. naturf. F. 2, 248.) Horses in the sweating condition sometimes emit light. Percy saw the wounds on a soldier's thigh continue phosphorescent for fourteen days; over the wounds of another, he saw a light like an ignis fatuus hover for six days. More frequently human urine just voided exhibits phosphorescence. (Jurine, Driessen, Gilb. 49, 291; 59, 262.)-Esser (Kastn. Archiv. 8, 414) saw the urine which he voided against the wall, when tired after a walk, exhibit phosphorescence; the wall shone for half a minute as if it had been smeared with phosphorus: the urine discharged two hours later was not phosphorescent. The urine of Viverra Putorius and Mephitis is likewise said to be luminous at the moment at which these animals void it. (F. D'Azora, Langsdorff.) The luminosity of the eyes of animals is due merely to reflected light. (Esser, Kastn. Archiv. 8, 399.)

II. Phosphorescence of Living Plants.

1. Sudden emission of Light.

A sudden flashing light is often emitted, on fine summer evenings, a little after sunset, by certain yellow flowers.

Such is the case with Tropaeolum majus, Tagetes patula and erecta, Calendula officinalis, Helianthus annuus, Lilium bulbiferum and Chalcedonicum, Polyanthes tuberosa, Oenothera biennis and Gorteria ringens: likewise Papaver orientale. (Elis. Linné, Abhandl. d. Schwed. Akad. 24, 291.-Haggren, N. Abhandl. d. Schwed. Akad. 9, 59.-Johnson, Schw. 31, 361.-Pursch, Flor. Amer, Septentr. 1, 261.-Green, J. Pharm. 18, 256.) Of these, Calendula emits the strongest light; then follows Trapaeolum, then Lilium bulbiferum and Tagetes patula, then Helianthus and Garteria. The same flower often gives out repeated flashes at intervals of several minutes. This light is undoubtedly electrical, perhaps

produced by the bursting of the pollen granules at the moment of fructification. (Zavadsky.) Ingenhouss, Senebier, and Saussure never observed this luminous appearance in Trapaeolum majus; neither could L. Treviranus discover it in Tagetes and other flowers; hence he regards the phenomenon as a mere illusion produced by the yellow colour of the flowers, which at night gives them an appearance of peculiar brightness.

Of a different nature from this is the flame observed by Ingenhouss, Bertholon, and Willdenow around the flowers of Dictamnus albus on the approach of a lighted candle-an appearance however which Schrank, Th. Saussure, Sprengel, and Treviranus were never able to discover. Biot (Ann. Chim. Phys. 50, 386) attributes this flame to the combustion of a volatile oil contained in the cells of the flower-stalks.

2. Steady Phosphorescence.

Some plants emit in the dark a faint continuous light, probably resulting from the formation of some substance which burns and emits light at ordinary temperatures, and consists, not of phosphorus, but more probably of a compound containing carbon and hydrogen.

The leaves of Phytolacea decandra have been observed to shine in September from 9 till 12 o'clock at night, sometimes with bluish green, sometimes with yellowish green light, accordingly as the current of air was stronger or weaker: they also remained luminous after being wiped. (K. v. Szäts A. Tr. 8, 2, 54.)

The acrid, milky juice of Cipó de Cananam (a plant growing in Brazil and probably belonging to the genus Euphorbia) emits light for several seconds when it flows from a wound in the plant. (Mornay, Gilb. 56, 367.)

Rhizomorpha subterranea stellata and aidalea, which grow in mines, emit light from their whole surfaces, but especially from the whitish growing points. The luminosity is brighter in young plants than in old ones; brighter also when they grow in warm, damp parts of the mine than in dry, cold situations: it is also increased when the plants are heated to 40° C. Rhizomorphs shine more brightly in oxygen gas than in common air. When they are immersed in this gas, together with a little water, they often continue luminous for nine days; and the oxygen gas is then found to be nearly consumed and converted into a somewhat smaller volume of carbonic acid. When these plants in the moist state have ceased to shine in the air, their luminosity cannot be restored by electric sparks or by oxygen gas: but it may often be restored by moistening the plant, when its cessation has been caused by dryness. The phosphorescence ceases in vacuo, but reappears when the air is admitted, even if the plant has remained in the vacuum for two hours. The plant likewise ceases to shine when placed in nitrogen gas, but regains its luminosity on being brought out into the air. In hydrogen, carbonic oxide, or chlorine gas, on the contrary, it loses its luminosity for ever, so that no light is emitted even when the plant is afterwards immersed in oxygen gas. (Bischof: Comp. Schw. 44, 65; also Laroche, Verh. d. Ges. naturf. Fr. Berlin, 1824, 1, 22.)

Rhizomorpha pinnata has been seen by Friesleben to emit light.

According to Linnæus, light is emitted by Byssus phosphorea (L) or Dematium violaceum. Pers.

According to Funk and Brandenburg, Schistostega osmundacea, a plant which grows in caverns, is phosphorescent. This is supposed by

Von Esenbeck to be the same moss which Gilbert (Gilb. 30, 242) saw shining with an emerald-green coloured light in a cavern in the Hartz. According to Ducluzeau, many confervæ growing near Montpelier are phosphorescent.

(b.) Phosphorescence of Putrefying Organic Bodies.

Many organic bodies emit light after death, sometimes before the commencement of actual putrefaction, sometimes simultaneously with it.

1. Phosphorescence of Putrefying Animals.

At a certain temperature, and in contact with moisture and oxygen gas, a decomposition appears to arise in many dead animals, especially in sea-fish, before the commencement of actual putrefaction,-producing a glutinous substance, whose constituents are capable of burning in the smallest quantity of oxygen, with a feeble light and scarcely perceptible development of heat:-or may it not be supposed that the decomposition is attended by the production of luminous infusoria?

Human corpses are very rarely phosphorescent. Of a body received on the 14th of February and dissected, one of the lower extremities, which remained over, began to exhibit phosphorescence on the 3rd of March. A second body brought into the same dissecting-room on the 5th of March likewise appeared luminous after a few days, first on the external and internal surface of the thorax, then on the abdomen, bones, tendons, and membranes, more faintly on the muscles, not at all on the viscera of the thorax. A portion of this second body laid upon a third rendered this also phosphorescent in two days, as if by contagion. The luminous matter, which appeared to be of an oily nature, could be removed in many places by the finger, on which it continued to shine. Placed under the microscope, it illuminated the whole field of view, and appeared to be in motion, like gamboge touched with water; but no animalcules were visible, excepting a minute Vibrio, such as is often observed in macerated bodies. The luminous substance continued to shine brightly in oxygen, carbonic oxide, phosphuretted hydrogen, and nitrogen gas-more faintly in carbonic acid-also with various degrees of brightness under water, milk and oil,-lost its phosphorescent power in a vacuum, but recovered it when the air was re-admitted, and was finally extinguished in sulphuretted hydrogen and chlorine gas, hot air, boiling water and alcohol. (A. Cooper and Appleton.)

Phosphorescence has likewise been observed in the flesh of oxen, calves, wethers, lambs, pigs, fowls, eagles, swallows, and serpents (Fabr. ab. Aquapendente, Boyle, Beale): in the case of ox-flesh, the phosphorescence ceased when actual putrefaction set in. (Bartholinus.) At Orleans in 1780, all the meat in a butcher's shop became phosphorescent. Veal, in October, three days old, cut up and beaten soft, but not yet stinking, emitted at a temperature between 12° and 18° C. a white light like phosphorus-was covered with a glutinous substance-imparted its luminous property to the fingers for a short time-continued to shine 24 hours later, at which time it began to smell badly-and even retained its luminosity, though feebly and only in particular places, after 48 hours, when the stench was much more powerful. (Buchner.)-Hen's eggs have also, on one occasion, been seen to emit light when opened.

Hulme produced phosphorescence in some very young tadpoles by preserving them in a solution of common salt and sulphate of soda.

Phosphorescence is also exhibited by Sepia officinalis, Loligo, and other species (in Sepia off, according to Spallanzani, the light does not attain its greatest intensity till putrefaction is completely set up); according tc Leuckart, by dead Aplysia, various species of Doris and Holothuria; according to Tiedemann, by dead sea-stars; according to Redi, by a Taenia; according to Redi, Spallanzani and Tilesius by medusas 24 hours after death; and according to an observation of Leo Allatius, by the refise

of dead crabs.

Luminosity is most readily exhibited by sea-fish, viz. Squalus Spinax and Pristis; Tetrodon Mola; Muraena Helena; Gadus Aeglefinus; Morhua Merlangus and virens; Coryphaena Hippurus; Cottus Scorpius and cataphractus; Pleuronectes Platessa; Scomber Scomber and Pelamis; Perca marina; Trigla volitans; Clupea Harengas; Salmo Salar and Trutta. Freshwater fish may, with some difficulty, be made to emit light, by rubbing them with salt and laying them in a moderately warm place. Heinrich, after many fruitless attempts, succeeded by this process in making the Esox lucius emit a very beautiful light, and the Silurus Glanis a faint light.

Phosphorescence shows itself in a day or two after the death of the fish, provided they are kept, neither boiled nor salted, in a moist condition, at a temperature of about 12° to 18° C. and in contact with air or oxygen gas. On the contrary, no phosphorescence is produced either in carbonic acid or sulphuretted hydrogen gas, or again when the fish are kept from contact of air by packing-in which case they may in winter be brought to the phosphorescent state by exposure to the air after they have been kept for fourteen days; e. g. Shell-fish. (Henrich.)

Phosphorescence begins at the head of the fish, particularly about the eyes, then extends to the belly, and lastly to the tail. (Martin, Schwed. Abhandl. 23, 224.) According to Dessaignes, the luminosity is most conspicuous on the aponeuroses, ligaments, capsules, and milts,-in short on the gelatinous parts, not on those of muscular structure. The internal parts do not emit light till they have been exposed to the air for a time. Sometimes there exudes from the animals a glutinous liquid, which is at first clear, but afterwards becomes thick and turbid, and then luminous. (Dessaignes.) This luminous slime may be spread upon the fingers and other foreign bodies. Hulme made a luminous solution of this substance in fresh water, sea-water, or a dilute solution of common salt, Glauber's salt, or sulphate of magnesia, by immersing the flesh of herrings or whitings in these liquids; after three days a luminous ring formed on the surface; when agitated, the whole mass of liquid became phosphorescent, and often continued so for several days.

According to Hulme, no rise of temperature is observable during the phosphorescence. According to Dessaignes, the phenomenon is accompanied by formation of carbonic acid in the air.

A freezing temperature interrupts the phosphorescence; a slight rise of temperature increases it; a boiling heat destroys it for ever. (Hulme.) -Abstraction of water destroys the luminosity of the fish; e. g. if it be suspended in a vessel containing quick lime. (Dessaignes.) The action of saturated solutions of various salts, alkalis, sulphuret of potassium, acids, alcohol, and ether may perhaps be similar; nevertheless, their lightdestroying power may also proceed from another cause-since dilute acids, even carbonic and hydrosulphuric acid, and likewise lime-water, destroy the phosphorescence. (Hulme.) The luminosity is increased in intensity, but shortened in duration, by dilute solutions of common salt, Glauber's