-

little tribes that have produced it, and denounces them as the most mischievous vermin in the ocean. But a tornado arises. the strength of the whirlwind is abroad-the clouds pour down a deluge over the mountains-and whole forests fall prostrate before its fury. Down rolls the gathering wreck towards the deep, and blocks up the mouth of that very creek the seaman has entered, and where he now finds himself in a state of captivity. How shall he extricate himself from his imprisonment?—an imprisonment as rigid as that of the Baltic in the winter season. But the hosts of the teredo are in motion: thousands of little augers are applied to the floating barrier, and attack it in every direction. It is perforated, it is lightened, it becomes weak; it is dispersed, or precipitated to the bottom; and what man could not effect, is the work of a worm. is it that nothing is made in vain; and that in physics, as well as in morals, although evil is intermingled with good, the good ever maintains a predominancy.

Thus

238

LECTURE XI.

ON THE BONES, CARTILAGES, TEETH, ARTICULATION, INTEGUMENTATION, HAIR, WOOL, SILK,

FEATHERS, AND OTHER HARD OR SOLID PARTS OF THE ANIMAL FRAME.

In a former lecture we took a general survey of the characteristic features that distinguish the unorganised from the organised world, and the vegetable kingdom from the animal: we examined into the nice structure of plants, and the resemblances which they bear to the animated form. In our last lecture we proceeded to an inquiry into the nature of the living principle, took a glance at a few of the theories that have been invented to explain its essence and mode of operation, and contemplated the origin and powers of the muscular fibre, which may be denominated its grand executive organ.

The muscles of an animal, however, are not the only instruments of animal motion; the bones, cartilages, and ligaments contribute very largely to the action, and the skin is not unfrequently a substitute for the muscle itself. These, therefore, as well as a variety of other bodies minutely connected with them, or evincing a similarity of construction, -as the teeth, hair, nails, horns, shells, and membranes, -are now to pass under our review, and are entitled to our closest attention; and I may add, that their diversity of uses and operations, and the curious phænomena to which they give rise, are calculated to afford not less amusement than instruction.

I had occasion to remark lately*, that lime is a substance absolutely necessary to the growth of man. It is, in truth, absolutely necessary to the growth of almost all animals; even soft-bodied or molluscous worms, except in a few instances, are not free from it; nay, even infusory animals, so minute as to be only discerned by the microscope, still afford a trace of it in the calcareous speck which constitutes their snout; but it is in the bones and shells of animals that lime is chiefly to be found; and hence those animals possess most of it in whom these organs are

most abundant.

Bone, shell, cartilage, and membrane, however, in their nascent state, are all the same substance, and originate from a viscid fluid, usually supposed to be the coagulable lymph, or more liquid part of the blood; which, secreted in one manner, constitutes jelly, or gelatine, a material characterised by its solubility in warm water, heated to about half the boiling point; and secreted in another manner, forms albumen, or the material of the white of the egg, characterised by its coagulating instead of dissolving in about the same heat: the difference, however, between the two, consisting merely, perhaps, in the different proportion of oxygene they contain. Membrane is gelatine, with a small proportion of albumen to give it a still certain degree of solidity; cartilage 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 se

* Vol. I. Series 1. Lect. VI. On Geology, p. 128. and passim; and Lect. VIII. On Organised Bodies, and the Structure of Plants compared with that of Animals, p. 152.

creted 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 as re-agents, 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 ear-rings, each of which was valued at upwards of eighty thousand pounds (centies sestertium), at a feast given to Marc 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

* This was on a trial who could give the most sumptuous banquet. Munacius Plancus was the arbiter. The expense of Marc 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 declared the victory to be hers. Plin. Hist. Nat. lib. ix. 35.

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