CORAL, (Encycl.) The nature and origin of coral has long been a subject of much dispute. Some have supposed that it is a stone; others a plant; and it has been almost universally believed that it was soft while in the sea, but grew hard on being taken out of it. But Boccone examined coral in the water, before it was taken up into the air, and invariably found it hard, except at its extremities, whence, by pressing it, flowed a small quantity of milky fluid, already taken notice of. We may therefore infer, that there is more of imagination than of truth in the name gorgonium, which the ancients gave to coral, and designed to show that Medusa's head did not convert objects into stone, more surely than coral became petrified as soon as it appeared in the air.
M. de Peyssonnel of Marcellies, has, in consequence of a series of experiments and observations from about the year 1720 to 1750, introduced a new system with respect to the nature and production of coral, and similar marine substances. Those bodies, which the count de Marisigli imagined to be flowers, this ingenious naturalist discovered to be insects inhabiting the coral; for upon taking branches of it out of the water, the flowers, which proceeded from a number of white points answering to the holes that pierced the bark, and the radiation of which resembled the flower of the olive-tree, entered into the bark and disappeared; but upon being again restored to the water, they were some hours after perceptible. These flowers spread on white paper lost their transparency, and became red as they dried. The holes in the bark correspond to small cavities upon the substance of the coral; and when the bark is removed, there may be seen an infinite quantity of little tubes connecting the bark with the inner substance, besides a great number of small glands adhering to them; and from these tubes and glands the milky juice of coral issues forth: the holes in the bark are the openings through which the insects that form these substances for their habitation come forth; and those cavities which are partly in the bark and partly in the substance, are the cells which they inhabit. The organs of the animal are contained in the tubes, and the glands are the extremities of his feet, and the milky liquor is the blood and juice of
of the animal, which are more or less abundant in proportion to its health and vigour. When the insects are dead, they corrupt, and communicate to the water the smell of putrid fish. This juice or liquor runs along the furrows perceived upon the proper substance or body of coral, and stopping by little and little becomes fixed and hard, and is changed into stone; and being stopped in the bark, causes the coral to increase proportionably and in every direction. In forming coral, and other marine productions of this class, the animal labours like those of the testaceous kind, each according to his species; and their productions vary according to their several forms, magnitudes, and colours.
The coral insect, or polype, M. Peyssonnel observes, expands itself in water, and contracts itself in air, or when it is touched with the hand in water, or acid liquors are poured upon it: and he actually saw these insects move their claws or legs, and expand themselves, when the sea-water containing coral was placed near the fire, and keep them in their expanded state when separated from the coral in boiling water. Broken branches of coral have been observed to fasten themselves to other branches, and have continued to grow; and this is the case, when they are connected with detached pieces of rock and other substances, from which no nourishment could be derived. The coral insects in their cells, not having been injured, continue their operations; and as they draw no nourishment from the stone of the coral, they are able to increase in a detached and separate state. Coral was found to be equally red in the sea as out of it; and it was more shining when just taken out of the water, than even when it is polished; and the bark by being dried becomes somewhat pale. M. Peyssonnel found that it grows in different directions, sometimes perpendicularly downwards, sometimes horizontally, and sometimes upwards; and in the caverns of the sea, open to every exposure.
This system was little regarded, though first communicated to the Academy of Sciences at Paris in 1727, till Mr Trembley's discovery of the fresh-water polype; but since that time, it has been confirmed by the observations of M. Bernard de Jussieu on the sea-coasts of Normandy, and those of M. de Reaumur near Rochelle. M. Donati of Turin has also adopted the same hypothesis, viz. that coral is a mass of animals of the polype kind; and instead of representing the polype beds and cells which they contain as the work of polypes, he thinks it more just to say, that coral and other coralline bodies have the same relation to the polypes united to them, that there is between the shell of a snail and the snail itself, or the bones of an animal and the animal itself.
The same system has also been excellently illustrated and established by Mr Ellis, in answer to the objections of Dr Baster of Zealand, and Dr Pallas of Berlin, who still refer corallines to the vegetable kingdom.
There are properly but three kinds of coral; red, white, and black: the black is the rarest, and most esteemed; but the red was formerly used in medicine. It must be chosen thick, smooth, and shining, and of a beautiful red, not covered with any tartareous matter. However, this substance is now scarce ever prescribed by any intelligent practitioner.