In most animals, there is connected with the muscles another kind of structure called tendon, which consists in a white substance very different from muscles, but having a fibrous structure. Although tendons are not necessary to the action of muscles, yet there are several advantages derived from them; they occupy much less room than muscles, and can be placed in greater numbers around the joints, so as to preserve the beauty and uniformity of the limbs. They may be considered as living cords, joining the muscle to the bone on which it is to act, and, being more scantily supplied with blood than muscles, make a smaller quantity of blood necessary to the system, which is certainly a convenience. Although the different parts of the body vary very much in their functions and degree of motion; yet, it is convenient, that they should be all united together by a substance of considerable elasticity. This is done by the interposition of cellular membrane, which is the general connecting medium throughout the body, attaching each organ to its neighbor, but allowing sufficient play for the performance of its function.
It is in the cellular membrane of different parts of the body that fat is deposited; and from the seeming caprice of nature, in overloading some animals, and entirely denying it to others, its use has been thought inconsiderable in the system. When, however, we remark, that fat is taken up in some diseases where the appetite is impaired; and that torpid animals, before hibernation, have a large quantity of it accumulated, and come out of that state quite emaciated: and that bees, who have no fat in their bodies, lay up a stock of food, having the same chemical properties, against their hibernating season; it appears very probable, that one use of fat is to form a reservoir of nutriment, which supplies the wants of an animal when food is not introduced by the stomach.
If we add the skin to the cellular membrane, we may say, without these the beauty and symmetry of the exterior would have been much diminished. We should have seen the raw muscles in all their actions, and the naked nerves exposed to the air and to injury. There would have existed deep fissures between the muscles, cavities in almost every part, and the body would have presented the sad appearance it now does in consumption.[198] But the cellular substance in some places only separates one part from another, or affords a slippery surface for one muscle to slide over the other: in others forming membranes or fascia to hide, to bind down and strengthen different organs; while in others admitting into its cells an oily substance, becomes fat, and fills up all the interstices, rounds off all prominences, softens acute lines, and gives a graceful softness and contour to the whole. And the skin enveloping in a close case, keeps all compact, and hides from the eye whatever might be offensive: while, at the same time the cutis or true skin serves for a surface for the nerves and exhalent vessels to terminate, the cuticle or scarf skin defends them from injury, and moderates their excessive sensibility.
As all animals are to live in media where the heat varies, it was necessary either to form them in such a way, that their functions should not be affected by varieties in temperature, or that they should be enabled to keep up the heat of their bodies at a regular point. Animals have been endowed with the latter power, and can accordingly maintain their heat, whether exposed to a high or low degree of temperature, with some exception as to the degree in the lower orders of animals, in some of which the temperature varies with that of the medium in which they are placed. This is the case with the Frog.—This animal, when placed in warm water, has the temperature of its body raised several degrees, and, on the other hand, may be reduced to the freezing point, without producing death. The heat of the human body, however, is little changed, whether it be exposed to intense cold, or much above the heat of boiling water. In the experiments made in heated rooms by Dr. Fordyce, and Sir Charles Blagden, these gentlemen remained several minutes in the heat of 260 degrees, nearly 50 degrees more than boiling water. At this heat a beefsteak and eggs were cooked near the stove, and yet the heated air produced no bad effect upon their bodies: it raised the temperature of their bodies only a few degrees.—The lungs are the chief agents by which heat is introduced into animal bodies. By their means, the blood is exposed to the air, and consumes its oxygenous part, which contains the principle of heat in a combined state. This, during circulation, is evolved by the minute blood vessels, so as to become sensible on every part of the body: and it is an important fact, that the quantity of oxygen consumed is greater in cold than warm weather; by this wise provision, in proportion as the heat is more quickly carried off by the coldness of the surrounding medium, the animal receives an increased internal supply. Many experiments have been instituted to ascertain the quantity of oxygen consumed in a given time by ordinary respiration, and, according to the best calculations, it appears that the consumption amounts to about 33½ ounces troy weight, in 24 hours; and it has been computed by philosophers, that the quantity of heat, which the oxygen consumes and will supply to the body, is nearly equal to that given out by a common candle.[199] I have thus attempted to give a short view of the different structures and functions of the body, and have briefly pointed out some of their varieties in the different classes of animals.
This corporeal system, which by its uniform and harmonious action contributes so essentially and largely to our terrestrial enjoyment, exhibits an astonishing display of the infinite wisdom, almighty power, and boundless goodness of its glorious Creator. Galen, an ancient Pagan physician, on contemplating the different parts of the human body, and the disposition of them, fell on his knees in humble adoration of the wisdom with which the whole is contrived; and was excited to challenge any one, after a hundred years’ study, to tell how the least fiber or particle could have been more commodiously placed, either for use or beauty. His seventeen books on the subject are like so many hymns of praise to the almighty and all-wise God, the Creator. Lactantius calls his writings on the body of man, a marvellous comment on his creation, and Galen himself managed the subject as a full demonstration of a Deity which every man carries about with him.
But what is still more deserving of our attention is the soul of man: for if the external structure be so admirable a piece of mechanism, what shall we say of the immaterial and intellectual spirit resident in it? This noble, constituent, essential part of man, is yet a more astonishing production of infinite skill and power. Elihu says, “The Spirit of God hath made me, and the breath of the Almighty hath given me life. There is a spirit in man, and the inspiration of the Almighty giveth them understanding.” God, by his creating energy, called all things out of nothing, but there was neither order, light, nor motion, till the Divine Spirit moved on the lifeless chaos; so the same all-wise and powerful Architect formed of clay the wonderful fabric of man’s body, which remained without life and action, till the Holy Spirit infused a vital spirit into him, thereby enduing him with sense, motion, understanding, will, and active powers. This soul, therefore, became a living principle of intelligence, consciousness, and activity, in man.
The great Creator said, “Let us make man in our image, after our likeness.” Now, as the Divine Being is infinite, he is neither limited by parts, nor definable by passions: therefore he can have no corporeal image after which he formed the body of man. The image and likeness in which he was created must necessarily be intellectual: his soul must have been formed after the nature and perfections of God. The Creator was now producing a spirit, formed after himself. He is the fountain whence it issued; hence the stream must resemble the spring which produced it.
The most perfect description of God, given to us in the Scripture, is that by our Saviour:—“God is a Spirit.” It has been observed by expositors, that this assertion is no where else to be found in the sacred Writings. That passage, “Now the Lord is that Spirit,” sounds something like it, but in meaning is different. The word God here is not to be understood personally, either for the Father, or the Son, or the Holy Ghost, alone, but essentially for the Divine Nature, which each of these glorious Persons possesses. The Divine Nature is spirit. This shows, that, according to the popular and common use of the word, he is a Being entirely separated from matter or body, in all its properties and affections; that he is a pure mind, and possessed of the most excellent powers and perfections, which belong to spiritual beings.
It is difficult, for persons of a low understanding, who are unaccustomed to abstract reflections, and who have imbibed their knowledge by means of the external senses, employed on material objects, to raise their minds to the contemplation of the existence of immaterial, invisible beings. But that there really are such, and particularly that God is such, admits of the clearest proof, and will not be called in question by any who on rational grounds acknowledge his existence. It is usually granted, that it is much more easy to say what a spirit is not, than to define what it is. It is not in the power of the wisest and most knowing of men, to declare its nature. Nay, who can explain what the consistence of any piece of matter is, which we every day see and touch!
But as, notwithstanding our ignorance of the essence of material objects, we are not only sure of their existence, but also know many of their properties; so in like manner, though we are ignorant of the nature of spirits, yet from their manifest operations and effects, we are both convinced that such beings exist, and have some notion of several of their faculties and powers.