is membrane, with a larger proportion of albumen to give it a still greater degree of solidity; and bone and shell are mere cartilage, hardened by the insertion of lime into their interior, the lime being secreted for this purpose by a particular set of vessels, and absorbed by the bony or shelly rudiments in their soft state. And hence any substances which, like the mineral acids, for example, have a power of dissolving the earthy matter of the two last, and of leaving the cartilage untouched, may be readily employed d'as reagents, to reduce them to their primary softness: and it was by this means that Cleopatra, as we are told by Pliny, dissolved one of the costly pair of pearls that formed her earrings, each of which was valued at upwards of eighty thousand pounds (centies sestertium), at a feast given to Mark Antony, and then presented it to him in a goblet, with an equal mixture of wine.*

In the adult state, however, as well as in the embryo state, it is necessary that the bones, like every other substance of the animal frame, should be punctually supplied with the elementary matter, or the means of forming the elementary matter, of which it essentially consists, the old matter of every kind being worn out by use, and carried away by a distinct set of vessels, called lymphatics or absorbents. It is the office of the digestive organs to receive such supply from without, and to prepare it for the general use. And hence, if we could conceive it possible for these organs, or any organs dependent upon them, to be so peculiarly diseased as to be incapable of preparing or conveying to the bones a sufficient quantity of lime (of which some portion is contained in almost every kind of food) to supply the place of that which is perpetually passing off, the necessary consequence would be, that the bones would progressively lose their hardness, and become cartilaginous and pliable. Now we sometimes do meet with the digestive or the secretory organs affected by such a kind of disease, and that both in children and adults. In children it is more common, and is called RICKETS; in grown persons it is simply called a SOFTNESS OF THE BONES, Or MOLLITIES OSSIUM. In the former case, the softened spine becomes bent from the weight of the head, and other extremities, which it is now no longer able to sustain, while the chest and most of the limbs partake of the general distortion. In the latter case many of the bones are sometimes reduced to imperfect cartilages, and can be bent and unbent in any direction.

Lime, however, is never found in the animal system in its pure state, and is certainly never introduced into it in such a state. It is usually combined with some acid, either the phosphoric, in which case the compound is called phosphate of lime; or carbonic acid gas, when it is called carbonate of lime, or common chalk.

It is of no small importance to attend to the nature of these two acids; for it is the difference between them that chiefly constitutes the difference between bones and shells; bones uniformly consisting of a larger proportion of phosphate of lime, or lime and phosphoric acid, and a less proportion of carbonate; and shells of a larger proportion of carbonate of lime, and a less proportion of phosphate. There are a few other ingredients that enter into the composition of both these substances, and which are chiefly obtained from the materials of common salt, as sulphuric acid and soda; but the proportions are too small to render it necessary to dwell upon them in a course of popular study. Bones, shells, cartilages, and membranes may therefore be regarded as substances of the same kind, differing only in degree of solidity from the different proportions that they possess of albumen and salts of lime.

Teeth, horn, coral, tortoise-shell, fish-scales, and the crustaceous integuments of crabs, millepedes, and beetles, are all compounds of the same elements combined in different proportions, and rendered harder or softer as they possess a larger or smaller quantity of calcareous salts; ivory and the

**This was on a trial who could give the most sumptuous banquet. Munacius Plancus was the arbiter. The expense of Mark Antony's, already bestowed, had been valued at just the price of this single pearl. Cleopatra was proceeding to dissolve its fellow, when she was suddenly stopped by the umpire, who de clared the victory to be hers. Plin. Hist. Nat. lib. ix. 35.

enamel of teeth possessing the largest quantity, and consisting almost exclu sively of phosphate of lime, with a small proportion of animal matter.

The gelatin and albumen are unquestionably generated in the animal system itself from the different substances it receives under the form of food; and it is curious to observe the facility and rapidity with which some animals are capable of producing them. The gastrobranchus cœcus, or hag-fish, a small lamprey-like animal of not more than eight inches long, will convert a large vessel of water in a short period of time into size or mucilage, of such a thickness that it may be drawn out in threads. The form and habits of this little animal are singular: Linnæus regarded it as a worm; but Bloch has removed it, and with apparent propriety, into the class of fishes. It is a cunning attendant upon the hooks of the fisherman; and as soon as it perceives a larger fish to be taken, and by its captivity rendered incapable of resistance, it darts into its mouth, preys voraciously, like the fabled vultures of Prometheus, on its inside, and works its way out through the fish's skin.

But though gelatin and albumen are unquestionably animal productions, the one a secretion from the blood, and the other a constituent principle of it, there is a doubt whether lime ought ever to be regarded in the same character. A very large portion is perpetually introduced into the stomach from without. In our lecture on the analogy between the structure of plants and of animals,* I had occasion to observe, that it forms an ingredient in common salt; not, indeed, necessarily so, but from the difficulty of separating the other ingredients from their combination with it: yet it enters not more freely into common salt than into almost every other article, whether animal, vegetable, or mineral of which our diet is usually composed. And upon this common fact it is more generally conceived, at present, to be a substance communicated to the animal frame, than generated by it.

This opinion, however, is by no means established; and there are many circumstances that may lead us to a contrary conclusion. Though almost every kind of food contains some portion of lime, it by no means contains an equal portion; and yet we find that a healthy young animal, whatever be the sort of food on which it is fed, will still provide lime enough from some quarter or other to satisfy the demand of its growing bones, and to maintain them in a due degree of solidity and hardness.

Again, the soil of some countries, as the mountains of Spain, for example, consists almost entirely of gypsum or some other species of limestone; while in other countries these are substances very rarely to be met with. It is a curious fact, that in that vast part of the globe which has been latest discovered, and to which modern geographers have given the name of Australia, comprising New-Holland and the islands with which its shores are studded, not a single bed or stratum of limestone has hitherto been detected, and the builders are obliged to make use of burnt shells for their mortar, for which I have lately advised them to substitute burnt coral. Now, it would be natural to suppose that the animals and vegetables of such a country would partake of the deficiency of its soil, and that the shells and bones which it produces would be less compact in their texture than those of other countries; yet this supposition is not verified by fact: nature is still adequate to her own work; the bones of animals are as indurated and perfect in these regions as in any parts of the old world; while the shells are not only as perfect, but far more numerous; and the frequent reefs of coral, altogether an animal production, that shoot forth from the shores in bold and massy projections, prove clearly that a coral rock, largely as it consists of lime, forms the basis of almost every island.

The prodigious quantity of lime, moreover, that is secreted by some animals at stated periods, beyond what they secrete at other times, seems to indicate a power of generating this earth in their own bodies. The stag, elk, and several other species of the deer-tribe, cast their antlers annually, and

*Series 1. Lect. viii.

tIt is understood that some beds of chalk have since been discovered on the farther side of the Blue Mountains, but none is still to be traced on the hither side in any of the settlements of the colony.

renew them in full perfection in about twelve weeks. These antlers are real bones; and those of the elk are sometimes as heavy as half a hundred pounds weight, and in a fossil state in Ireland have been dug up still heavier, and of the enormous measure of eight feet long, and fourteen feet from tip to tip; on beholding which, we may well, indeed, exclaim with Waller,—

O fertile head! which every year

Could such a crop of wonders bear.

In like manner, many species of the crab and lobster tribes annually throw off and renew the whole of their crustaceous covering, and apparently without any very great degree of trouble. The animal at this time retires to some lonely and sheltered place, where, in its naked and defenceless state, it may avoid the attack of others of the same tribe which are not in the same situation: a line instinctively drawn now separates the shell into two parts, which are easily shaken off, when the secernent vessels of the skin pour forth a copious efflux or sweat of calcareous matter all over the body, the more liquid parts of which are as rapidly drunk up by the absorbent vessels, so that a new calcareous membrane is very soon produced, which as speedily hardens into a new calcareous crust, and the entire process is completed in about a fortnight. This genus, also, in many of its species, is capable of reproducing an entire limb, with the whole of its calcareous casing, whenever deprived of it by accident or disease, or it voluntarily throws it off, as I have already observed it is capable of doing, to extricate itself from being seized hold of; though the new limb is seldom so large or powerful as the original. So, in other animals, we sometimes find a large and preternatural secretion of calcareous matter, in consequence of a diseased habit of particular organs, or of the system generally. The human kidneys are too often subject to a morbid affection of this kind, whence a frequent necessity for one of the most painful operations in surgery. The chalkstones, as they are erroneously called, that are often produced in protracted fits of gout and rheumatism, are rather lithate of soda than any compound of lime; but instances are not wanting in which one of the lungs has been found converted into an entire quarry of limestone.

In the Transactions of the Royal Society there are several cases related of young persons who, in consequence of a morbid habit, threw out a variety of calcareous excrescences, either over the hands and feet, or over the whole body;* and about four years since, a Leicestershire heifer was exhibited for a show in this metropolis, the head and neck of which were completely imbedded in horny excrescences of this kind, and the back and limbs profusely sprinkled over with them: some of the horns, and especially those about the dew-lap, were as long and as large as the natural horns of the forehead, but they were much more calcareous and brittle. A calcareous scurf, moreover, was secreted over every part of the skin, which, whenever the skin was scratched or bitten, united with the fluid that oozed forth, ramified, and divaricated into masses of small roses. At the request of the proprietor I took an account of this extraordinary animal, and have since communicated it to the Royal Society. In all other respects it was in good health; its size was proportionate to its age, and its appetite enabled it to digest foods of every kind equally; and though, in consequence of this, its diet had been frequently varied, the propensity to a secretion of calcareous matter continued the same under every change.

It appears, therefore, very doubtful whether the animal economy be not at times capable of generating lime, as well as gelatin or albumen, out of the different materials introduced into the stomach in the form of food. Vauquelin endeavoured to decide the question by a variety of experiments upon the nature of the egg-shells of a sitting hen, and an examination into the proportion of calcareous matter contained in a given weight of shells, compared with the calcareous matter furnished by her food, and that discharged as a

* See also Mr. Baker's account of the porcupine-man, Phil. Trans. for 1755

recrement; and, so far as these experiments go, they support the opinion of a generation of lime, and that in very considerable abundance, the weight secreted appearing to have been five times as much as that introduced into the stomach. But to determine the question incontrovertibly requires so nice a precision in the mode of conducting such experiments, as from a variety of circumstances, it seems almost impossible to attain.

It is to the power which the living principle possesses, either of secreting or generating the substance of lime by its natural action, that we are indebted for all those elegant shells that enrich the cabinet of the conchologist, and seem to vie with each other in the beauty of their spots, the splendour and irridescence of their colours, and the graceful inflection of their wreaths. And it is to the power which the same principle possesses, of forming this substance by a morbid action, that we owe not only those unsightly excrescences I have just mentioned, but some of the most costly ornaments of superstition or luxury: those agate-formed bezoards which in Spain, Portugal, and even Holland were lately worn as amulets against contagion, and which have been let out for hire at a ducat a day, and been sold as high as three hundred guineas a piece; and those delicate pearls which constitute an object of desire among the fair sex of every country, and which give additional attraction to the most finished form.

The first are usually obtained from the stomach or intestines of the goat or antelope; in the latter case being called oriental bezoards, and possessing the highest value. The most esteemed are those obtained from the stomach of that species of the oriental antelope called the gazel, to which the Persian and Arabian poets are perpetually adverting whenever they stand in need of an image to express elegance of form, fleetness of speed, or captivating softness of the eyes. The second are obtained from the inside of the shells of the mytilus margaritiferus and mya margaritifera, pearl-muscle and pearloyster; the former, producing the largest and consequently the richest, is found most commonly on the coast of Ceylon; the latter not unfrequently on that of our own country, and was traced some centuries ago in great abundance in the river Conway in Wales. Linnæus is said to have been acquainted with a process by which he could excite at pleasure a secretion of new pearls in the pearl-oysters which he kept in his reservoirs. It is generally supposed to be a diseased secretion somewhat similar to that of the stone in the human bladder.

The murex tritonis, or musical murex, is here also worth noticing. Its calcareous shell is ventricose, oblong, smooth, with rounded whorls, toothed aperture, and short beak, about fifteen inches long, white, and appearing as if covered with brown, yellow, and black scales. It inhabits India and the South Seas, and is used by the New-Zealanders as a musical shell, and by the Africans and many nations of the East as a military horn.

Before we quit this subject, I will just observe, that it is to the same tribe we are indebted for our nacre or mother-of-pearl which is nothing more than the innermost layers of the shell, in which the morbid works or concretions which we call pearls lie imbedded; and that to the same order of shells the Indians owe their wampum or pieces of common money, which are formed of the Venus mercenaria, or clam-shell, found in a fossil state; and that our own heralds owe the scallop, ostrea maxima, that so often figures in the field of our family arms, and was formerly worn by pilgrims on the hat or coat, in its natural state, as a mark that they had crossed the sea for the purpose of paying their devotions at the Holy Land.

From these facts and observations we cannot but behold the great importance of lime in the construction of the animal frame, the extensive use which is made of it, and the variety of purposes to which it is applied: combined in different proportions with gluten and albumen it affords equally the means of strength and protection, produces the bones within and the shells without, the external and internal skeleton, and is discoverable in every class, order, and even genus of animals, except a very few of the soft worms and insects in their first and unfinished state.

It is hence the cerambyx, and several other tribes of insects, are able to make that shrill sound which they give forth on being taken, and which appears like a cry from the mouth, but is in reality nothing more than the friction of the chest of the insect against the upper part of its abdomen and wingshells. And it is hence, also, that the ptinus fatidicus, or death-watch, produces those measured strokes against the head or other part of a bed in the middle of the night, which are so alarming to the fearful and superstitious; but which, in truth, are nothing more than a call or signal by which the one sex is enticed to the other, and is merely produced by the insect's striking the bony or horny front of its head against the bed-post, or some other hard substance.

Having, then, taken a brief survey of the elementary nature and chemical composition of these harder parts of the animal frame, I shall proceed to make a few remarks upon the relative powers of each, and their diversified applications amid the different kinds of animals in which they are employed.

The BONES in their colour are usually white; but this does not hold universally, for those of the gar-pike (esox belone) are green; and in some varieties of the common fowl they approach to a black: Abelfazel remarks this of the fowls of Berar, and Niebuhr of those of Persepolis.

The bones of an animal, wherever they exist, are unquestionably the levers of its organs of motion: and so far the mechanical theorists are correct. In man and quadrupeds, whose habits require solidity of strength rather than flexibility of accommodation, they are hard, firm, and unpliant, and consist of gluten fully saturated with phosphate and carbonate of lime. In serpents and fishes, whose habits, on the contrary, demand flexibility of motion, they are supple and cartilaginous; the gluten is in excess, and the phosphate of lime but small in proportion to it, and in some fishes altogether deficient in the composition of their skeleton, though still traceable in their scales and several other parts. In birds, whose natural habits demand levity, the bones are skilfully hollowed out and communicate with the lungs, and instead of being filled with marrow are filled with air, so that the purpose for which the structure of birds was designed is as obvious, and as deeply marked, in the bones as in the wings, whose quills also are for the same reason left hollow, or rather are filled with air, and in many tribes communicate with the lungs as the bones do.

*

The skeleton of the cuttle-fish (sepia officinalis) is extremely singular: its back bone, for some purpose unknown to us, is much broader than that of any other aquatic animal of the same size, and of course would be much heavier but for a curious contrivance to prevent this effect, which consists in its being exquisitely porous and cellular, and capable, like the bones of birds, of becoming filled with air, or exhausted of it, at the option of the animal, in order to ascend or descend with the greater facility. It is an animal of this kind, or closely akin to it, that inhabits the shell of the beautiful paper-nautilus, and still more beautiful pearl-nautilus (argonauta and nautilus tribes), and which hence obtain no inconsiderable portion of that lightness which enables them, with their extended sails, to scud so dexterously before the wind, In the calamary (sepia loligo) we meet with an approach towards the same contrivance, in a kind of leafy plate introduced into the body of the animal; and even in the cloak of the slug-tribe we trace something of the same sort, though proportionably smaller, and verging to the nature of horn.

Generally speaking, the bones grow cartilaginous towards their extremities, and the muscles tendinous; by which means the fleshy and osseous parts of the organs of motion become assimilated, and fitted for that insertion

*The animal has commonly been supposed to be a real sepia or cuttle-fish; but several naturalists have of late doubted this, inasmuch as there are a few marks of distinction that seem to take it out of this genus. Rafinesque has hence made another genus, for the purpose of receiving those which possess these distinctive signs; and Dr. Leach has lately distinguished it specifically, in consequence of specimens sent home from the unfortunate Congo expedition as collected by Cranch, by the name of Ocythoe Cranchi Even this animal, however, is regarded as a parasite in the shell, and only possessing it when empty. The proper animal is not known to the present hour.-See Phil. Trans. 1817, p. 293.