(according to the several parts each may be destined to nourish) earthy matter, or fibrine, or fluids of various compositions, density, and transparency these are facts, the causes of which ingenuity fails to unravel, and in which conjecture is lost.

With respect to the nutrition of animals, this observation will, we think, be found generally to hold good, viz. that animals require for their support, particles which have immediately belonged to, and formed part of, organized bodies, either of the animal or vegetable kingdom; being, as we may hence conclude, unable to assimilate particles belonging immediately to bodies purely inorganic: and it would seem also, that animals derive a larger proportion of nutritive matter from bodies whose composition is similar to their own, that is, from other animals, than from vegetable substances. Now, although the natural food of many animals consists entirely of vegetable matter, yet we see that such require and consume a much larger quantity in proportion, than carnivorous animals, which make flesh their food. For instance, the weight of matter requisite for the support of a carnivorous animal, is infinitely less than what a graminivorous animal of even a smaller bulk would require. Hence we may conclude, that all substances, before they become fitted for the nutrition of the animal race, must undergo a peculiar change and modification,-in fact, become organized; and that in the flesh of animal bodies, the relative proportion of nutriment is greatest.

If this be the case, that all matter, before it be fitted to support animal life, must itself have been immediately in a state of previous organization, it may be asked, Does not the vegetable world also follow the same law? No: The great Author of the universe has so constructed the vegetable tribes, that they are enabled to convert the particles of inorganic matter into organic bodies; to assimilate various earths, water, and air, which, becom

it were, the first stamp of organization, and enter upon their career of vitality; the soil, however, necessary for the growth and nutrition of many plants, does indeed contain a great proportion of decomposed animal or vegetable matter; but this forms no objection: for, in the first place, animal or vegetable bodies lose by putrefaction all claim to be considered as organized; and, in the second place, it would appear, that it is by the peculiar gases arising from such decomposed matter, that vegetables are nourished, whereas animals require recent vegetables or animal matter, for their support. Thus does it appear, that one of the purposes for which the vegetable kingdom is designed, is to form a vast laboratory, in which various inorganic substances are to be prepared for the use of the animal world, by effecting upon them a necessary, peculiar and most wonderful change; a step preparatory to a new change as wonderful-for a particle of matter, originally unorganized, may become a portion of the grass which covers the meadow,-of the ox which grazes upon it,-of man, the lord of the creation,-and when he moulders in the earth, return to its original state, and again become incorporated in plants, to run a new career.

It has been stated, that the animal frame owes its existence and growth to the appropriation and assimilation of fresh particles, which become identified with the rest of the body; let us explain how this is effected :-Proceeding from the inner surface of the stomach and the intestines, numerous small tubes or vessels are observable, whose office it is to separate and absorb, or take up, the nutritive particles of the food, as prepared by the digestive organs for their reception: this nutritious portion is called the chyle. When the food has entered the stomach, it becomes mixed with saliva, and the gastric juice. By the agency of these it becomes converted into an uniform pulpy mass, to which the name of chyme is given; but it is not

yet fitted for the system; it now passes through the pyloric orifice of the stomach into the duodenum, (a portion of intestine,) and becomes there mixed with the pancreatic juice and bile. The pancreatic juice is a fluid prepared by a gland termed the pancreas, the bile by the liver. By the action of these fluids on the pulpy mass, a complete conversion is effected, and that portion fitted for the purposes of the animal economy is, as we have said, termed chyle. If we examine the state of these minute tubes or vessels in an animal recently killed, and before the vital warmth is extinguished, we shall see them (at least if the animal has been lately fed) filled with a milky fluid, from whence they have their name lacteals: this milky fluid is the chyle.

The lacteals having thus absorbed this nutritive portion of the food, after communicating freely with each other, pass through certain glands termed mesenteric, where the chyle appears to acquire new properties. Emerging from these glands, the lacteals carry the chyle onwards, till they enter, at last, into the thoracic duct, a vessel which passes along the spine, and pours the chyle into a large vein, almost immediately entering the heart, termed the left subclavian vein; here it becomes mingled with the blood. It has not yet, however, lost its character; but after passing through the heart, and thence through the lungs, it becomes incorporated with the rest of the blood, from which it is no longer to be distinguished.

There is, however, another set of vessels, which, as well as the lacteals, terminate in the thoracic duct, and contribute likewise to the repair and preservation of the system.

Throughout every part of the frame, in the interior as well as on the surface, are distributed innumerable vessels, destined to absorb and carry into the blood the superfluous fluids of the body, as well as all substances immediately within the sphere of their action. External bodies are not the only ones on which they act.

On the structure of the frame itself their operations are continually carried on; for it must not be forgotten, that the organized living machine is undergoing a double set of internal operations, its destruction and renovation; and whatever comes off in the constant wear of this machine is taken up by these vessels, the absorbents, or, as they are called, lymphatics, from the limpid fluid we always observe them to convey.

The minute tubes which form the commencement of the lymphatics, are furnished with orifices so small as to be totally imperceptible to the naked eye; and each orifice, endowed with the power of contracting or dilating, absorbs or refuses, according to the peculiar impression produced by the object in contact.

In what manner the lymphatics, and indeed the whole absorbent system, propel or convey the fluids they contain, is a question on which physiologists have entertained very different views; some, for instance, and these eminent men, have asserted it as a fact, that fluids circulate through and ascend these minute tubes, contrary to the law of gravitation, not from any propelling power in the tubes themselves, but by that principle which causes the ascent of liquids through tubes of great minuteness, termed capillary attraction. To this opinion, however ingenious and apparently satisfactory, there are many strong objections: for were it correct, we might expect that neither age, nor sex, nor temperament, nor habit, would produce the least variation or irregularity in the absorbing power, and that all would proceed with uniformity. But this is far from being the case; for as much so as every vital function, the action of the absorbents is liable to irregularities inconsistent with the theory just mentioned. Indeed it is much to be doubted whether any of the functions of organized bodies, on which their vital existence depends, are to be accounted for upon purely mechanical principles; a supposition which has led to theories very

ingenious, but unfortunately errone

ous.

It appears more possible, according to our ideas, that the absorbent vessels are endowed with a sufficient power of carrying on or propelling the fluids they contain, by some peculiar action in themselves, which they are enabled to exert so as to answer the end in view.

The lymphatics, after arising from various parts of the frame, the surface as well as the interior, by minute tubes in close contact, unite and divide, and so intermingle with each other as to form a close network, which, with a similar tissue of nerves and blood-vessels, forms the cellular and membranous textures of the body. Emerging thence, and proceeding onwards, they form distinguishable trunks, and again enlarge by the union of others; and multitudes of these run together a parallel course, forming companies proceeding from different quarters, and by different routes, for the same destined place; the whole, however, communicating largely with each other.

In various parts, and for reasons not fully known, companies of these absorbents form themselves into masses of convolutions, differing in number and magnitude, and intermingled with a similar congeries of blood-vessels. These masses are the glands, (observed in the neck and other parts,) the uses of which are not, as yet, fully ascertained, although it is most probable that some change is effected by their agency on the lymph, by which it is rendered more fit for the purposes of the animal frame; and this would further appear, from the increased tendency to coagulate, which it manifests after passing through the glands, (which it does slowly, as if impeded by the way,) as well as some alteration in its appearance.

At the same time, however, it must be observed, that the real nature of the lymph is far from being well understood. By some it is considered as analogous to the serum of the blood, which is indeed the opinion of

Hâller, who often gives the name of lymph indiscriminately to the fluid of the absorbents, and to the serum of the blood.

From the circumstances attending the production of the lymph, we might be led to judge, that its nature and component parts would be subject to variety and change; and this is found to be the case; but in the chyle these differences are still more evident, arising from the various substances used as food. Indigo, madder and beet-root tinge it with their respective hues. It is, however, as we have said, in general white, slightly viscid, and much resembles milk. When removed from its vessels and exposed to the air, it separates into two parts, viz. fibrine and serum :—and the lymph also, under similar circumstances, undergoes the same change.

Both the lacteals and lymphatics terminate in the thoracic duct, which empties its contents into the left subclavian vein. At the point of junction between these a valve is placed, so constructed as effectually to prevent the blood from finding its way into the thoracic duct, but which offers no impediment to the exit of the chyle.

From this source then the blood receives its supplies, and nothing can incorporate with the system, or be received into it, without proceeding through this channel.

Having now conducted the nutriment through its various stages, till it enters into the blood to supply the continual drain upon this reservoir of vitality, we shall follow up the subject, and proceed to give a more detailed account of that most beautiful and interesting phenomenon of the animal frame, the circulation of the blood.

The circulation of the blood is an operation immediately connected with our existence, and on which it depends; and will it not excite our astonishment, that two centuries have scarcely elapsed since its laws have been at all correctly ascertained? and even now, many points are disputed, and enveloped in obscurity. We may with safety conclude, that the ancients