how the secretion is furnished, and the nature of its constitution, but likewise its application to other operations.

Lastly, since from the commencement of life to its termination, the component parts of the body are never the same, but constantly receiving fresh accessions of matter, and rejecting the old and decayed particles, numerous vessels are incessantly engaged in the secretion of the various textures composing the different organs of the body. Thus, in bone the osseous tissue is secreted; in muscle the muscular fibre; in glands their peculiar tissues, and so forth. In every individual part the vessels furnish the characteristic matter required in due quantity, and with the necessary quickness of renewal. After examining the various conservative organs and functions, we shall next turn our attention to those of relation.

The Nervous System will first be taken into consideration. In the brain we shall find the organ in which mind and matter become more immediately associated with each other-the especial seat of perception-the source from whence spring the purposes of the will—the throne of the intellectual powers, such as judgment, memory, and reflection.

The nerves will be found to be subservient to various purposes; some of them belonging to the special organs of sense, as sight, hearing, and smell; others conveying the commands of the will in order to bring into action the muscles that obey its influence; others transmiting to the seat of perception the impressions made upon the different parts of the body; while some are connected with instinctive movements; and others, again, appear to be more immediately subservient to organic life.

The knowledge we possess of the mode of action of the different parts of the nervous system is less clear and determined than of most other parts of the body. Yet the functions to which they evidently contribute are of such high and paramount importance:-they are so essential to the exercise of other organs, contribute so much

to the combination of the different parts of the system into one harmonious whole, and are so characteristic of the higher organized animals, that their structure and uses cannot fail to excite interest. Although, therefore, we may be unable to point out the uses of the various parts, we shall endeavour to give such an account of their structure and distribution as may convey to the general reader a correct view of the whole. At the same time we shall be cautious in entering upon the merits of the various discordant opinions that have been and are at present entertained respecting this interesting portion of the animal frame.

The organs of the five external Senses will in the next place occupy our attention. The construction of these instruments is so admirable, the uses of many of their parts so obvious, and the beauty of the mechanism so striking, that they have attracted the attention of the most superficial observer. In tracing the connexion between the mechanism and the result of its action, it will be a pleasing task to point out the many evidences of design afforded, the excellency of the contrivances, and how much these senses contribute to the preservation, enjoyment, and welfare of the animal.

The means by which animals are enabled to re-act upon the external world, to perform the various motions so essential to the exercise of various other functions, to avail themselves of the power of locomotion, to fix their attitudes, and to vary their postures and gestures, depend upon the Muscular System;-in connexion with which we shall consider the bones, the manner in which they are bound together by ligaments, and several other structures that contribute to these purposes.

Before leaving the animal mechanism, we shall direct our attention to the various steps of its Formation and Development, from its first rudimentary state, while it is still connected with the parent, till its final separation from the principle of life in old age, and when in death

the body is yielded up to mechanical and chemical influences and laws.

Many of the functions of the human body would have been still unknown and unappreciated, had it not been from observations made on the structures and uses of the different parts in the lower animals: indeed these yet afford the principal sources from whence the facts are derived, not only for confirming what has been already ascertained, but for affording the means for extending physiological knowledge. The functions in the human body have long ceased before we can presume to examine them. But in the lower animals it is different: we are able to examine them even in the living state; we can place them in various conditions best calculated to exhibit them in action; and, moreover, we obtain valuable information from the various modifications of structures as to size, proportion, and relation in the different classes, orders, and families of animals. Accordingly, we shall avail ourselves of these rich sources of physiological truth, and advert to the numerous interesting and curious contrivances displayed in these structures, wherever they seem calculated to throw light on corresponding organs and functions in the human subject.

The study of no department of science affords so many clear, striking, and irresistible proofs of the attributes of the deity, as that which has for its object the consideration of the animal structure, and the mode in which its functions are carried on. Take, for example, any single organ of the animal machinery—the eye, or the ear, or the organ of voice-examine its mechanism, study its adaptation to the office it has to perform, observe it in operation; and where can there be found more direct, more explicit, and more irrefragable evidence of foresight in the design, benevolence in the purpose, and wisdom in the contrivance? It is said to have been in consequenee of such studies that the celebrated Grecian physician and philosopher Galen breaks forth in the following beautiful

apostrophe—“ In explaining these things," he says, "I esteem myself as composing a solemn hymn to the author of our bodily frame, and in this I think there is more true piety than in sacrificing to him hecatombs of oxen and burnt-offerings of the most costly perfumes; for I first endeavour to know him myself, and afterwards to show him to others, to inform them how great is his power, his wisdom, his goodness."

However worthily Galen thus expresses himself when contemplating the Great Author of all, and however far in this respect he surpasses the most distinguished of his heathen predecessors in a rational view of the character and proper worship of the Deity, it is not to be forgotten that though educated amidst the darkness of idolatry, and although there be no reason to believe that he ever laid aside its delusions, yet he was born in A. D. 131, at Pergamos, where was established one of the seven churches of Asia, and where the gospel had already widely spread. It is impossible to conceive of a man of his acute, inquisitive, and penetrating mind, with such a thirst as he displayed for the acquisition of truth, that he could have overlooked, or have been altogether ignorant of the light which had already begun to shine forth around him, and which was to dissipate the darkness and gloom that had so long overwhelmed the intellect of man, as if to sow that however great the original talents and endowments, however vast the acquirements, or however penetrating the judgment, these of themselves could never have attained to a just conception of the condition of man, and the true character of the Creator and Preserver of the universe.

But when a knowledge of God has been obtained from higher sources, how much does the contemplation of his works, as displayed in the animal economy, contribute to confirm the truth that is revealed! how numerous are the instances afforded of superintending providence, of infinite power, of universal beneficence, wisdom, and foresight!

CHAPTER I.

CIRCULATION.

General View of Circulation-Opinion of Hippocrates-Theory of Harvey-Discovery of the Absorbents-Structure of the Heart-Condition at the point of death-Structure and Action of the Arteries-Of the Capillaries-Of the Veins -Operation of Transfusion-Heart an involuntary organ-Heart insensible -Effects of the Passions of the Mind-Size of the Heart in proportion to the other Organs-Mechanical conditions of the Blood Vessels-Circulation influenced by Respiration-through the Brain-in the Abdomen.

In all animals the blood is subjected to motion, more or less rapid in each after its own kind; the agents by which the motion is produced, and the channels through which the blood is conveyed, being most perfectly adequate to the purposes intended, and these purposes admirably adapted to the circumstances under which the animal is destined to be placed. In the more highly organized beings, such as man, mammalia, and birds, from birth throughout life, the agents which put the blood in motion are constructed upon the same general plan, and produce results similar in all. An acquaintance, therefore, with the structure in one species will enable us to acquire a correct general notion of what obtains in the whole. The description we have now to submit will have especial reference to the organs of the circulation of the blood in These instruments are the heart, arteries, capillaries, and veins, A general view of these in the first

man.

B