Anatomy and Physiology

The general object of both these sciences is, to investigate and describe the structure and economy of the animal frame.—Anatomy dissects dead bodies. Physiology investigates the functions of page 109 those that are living. The former examines the fluids, muscles, viscera, and all the other parts of the human body, in a state of rest; the latter considers them in a state of action.

The parts of the human body have been distinguished into two different kinds—solids and fluids. The solid parts are, bones, cartilages, ligaments, muscles, tendons, membranes, nerves, arteries, veins, hair, nails, and ducts, or fine tubular vessels of various kinds. Of these solid parts, the following compound organs consist: the brain and cerebellum, the lungs, the heart, the stomach, the liver, the spleen, the pancreas, the glands, the kidneys, the intestines, the mesentery, the larynx, and the organs of sense—the eyes, ears, nose, and tongue. The fluid parts are, the saliva, or spittle, phlegm, serum, the chyle, blood, bile, milk, lympha, urine, the pancreatic juice, and the aqueous humor of the eyes. The human body is divided into three great cavities—the head; the thorax, or breast; and the abdomen, or belly. The head is formed of the bones of the cranium, and incloses the brain and cerebellum. The thorax is composed of the vertebrae of the back, the sternum, and true ribs; and contains the heart, the pericardium, the breasts, and the lungs. The abdomen is separated from the thorax by means of the diaphragm, which is a fleshy and membranous substance, composed for the most part of muscular fibers. This cavity is formed by the lumbar vertebræ, the os sacrum, the ossa innominata, the false ribs, the peritoneum, and a variety of muscles. It incloses the stomach, intestines, omentum, or caul, the liver, pancreas, spleen, kidneys, and urinary bladder.—Without attempting any technical description of these different parts, which could convey no accurate ideas to a general reader, I shall merely state two or three facts in relation to the system of bones, muscles, and blood-vessels, as specimens of the wonderful structure of our bodily frame.

The Bones may be regarded as the propwork or basis on which the human body is constructed. They bear the same relation to the animal system, as the woodwork to a building. They give shape and firmness to the body; they support its various parts, and prevent it from sinking by its own weight; they serve as levers for the muscles to act upon, and to defend the brain, the heart, the lungs, and other vital parts from external injury. Of the bones, some are hollow, and filled with marrow; others are solid throughout; some are very small; others very large; some are round, and others flat; some are plane, and others convex or concave;—and all these several forms are requisite for the situations they occupy, and the respective functions they have to perform.—The spine, or back-bone, consists of 24 vertebrae, or small bones, connected together by cartilages, articulations, and ligaments; of which 7 belong to the neck, 12 to the back, and 5 to the loins. In the center of each vertebra, there is a hole for the lodgment and continuation of the spinal marrow, which extends from the brain to the rump. From these vertebrae the arched bones called ribs proceed; and seven of them join the breast-bone on each side, where they terminate in cartilages, and form the cavity of the thorax or chest. The five lower ribs, with a number of muscles, form the cavity of the abdomen, as above stated. The spine is one of the most admirable mechanical contrivances in the human frame. Had it consisted of only three or four bones, or had the holes in each bone not exactly corresponded, and fitted into each other, the spinal marrow would have been bruised, and life endangered at every bending of the body. The skull is composed of 10 bones, and about 51 are reckoned to belong to the face, the orbits of the eyes, and the jaws in which the teeth are fixed. There are seldom more, than 16 teeth in each jaw, or 32 in all.—The number of bones in a human body is generally estimated at about 245; of which there are reckoned, in the skull, head, and face, 61; in the trunk, 64; in the arms and hands, 60; and in the legs and feet, 60. The bones are provided with ligaments, or hinges, which bind and fasten them together, and prevent them from being displaced by any violent motion; and, that the ligaments may work smoothly into one another, the joints are separated by cartilages, or gristles, and provided with a gland for the secretion of oil, or mucus, which is constantly exuding into the joints; so that every requisite is provided by our Benevolent Creator, to prevent pain, and to promote facility of motion. “In considering the joints,” says Dr. Paley, “there is nothing, perhaps, which ought to move our gratitude more than the reflection, how well they wear. A limb shall swing upon its hinge, or play in its socket, many hundred times in an hour, for sixty years together, without diminution of agility; which is a long time for anything to last, for anything so much worked as the joints are.”

The Muscular System.—A muscle is a bundle of fleshy, and sometimes of tendinous fibers. The fleshy fibers compose the body of the muscle; and the tendinous fibers the extremities. Some muscles are long and round; some plain and circular; some have spiral, and some have straight fibers. Some are double, having a tendon running through the body from head to tail; some have two or more tendinous branches running through, with various rows and orders of fibers. All these, and several other varieties, are essentially requisite for the respective offices they have to perform in the animal system. The muscles constitute the fleshy part of the human body, and give it that varied and beautiful form we observe over all its surface. But their principal design is, to serve as the organs of motion. They are inserted, by strong tendinous extremities, into the different bones of which the skeleton is composed; and by their contraction and distention, give rise to all the movements of the body. The muscles, therefore, may be considered as so many cords attached to the bones; and the Author of Nature has fixed them according to the most perfect principles of mechanism, so as to produce the fittest motions in the parts for the movements of which they are intended.

One of the most wonderful properties of the muscles is, the extraordinary force they exert, although they are composed of such slender threads, or fibers. The following facts in relation to this point, are demonstrated by the celebrated Borelli, in his work, “De Motu Animalium.” When a man lifts up with his teeth a weight of 200 pounds with a rope fastened to the jaw-teeth, the muscles named Temporalis and Masseter, with which people chew, and which perform this work, exert a force of above 15,000 pounds weight. If any one hanging his arm directly downward, lifts a weight of 20 pounds, with the third or last joint of his thumb, the muscle which bends the thumb, and bears that weight, exerts a force of about three thousand pounds. When a man, standing upon his feet, leaps or springs upward to the hight of two feet, if the weight of such a man be 150 pounds, the muscles employed in that action will exert a force 2000 times greater; that is to say, a force of about three hundred thousand pounds. The heart, at each pulse or contraction, by which page 110 it protrudes the blood out of the arteries into the veins, exerts a force of above a hundred thousand pounds. Who can contemplate this amazing strength of the muscular system, without admiration of the power and wisdom of the Creator, who has indued a bundle of threads, each of them smaller than a hair, with such an astonishing degree of mechanical force! There have been reckoned about 446 muscles in the human body, which have been dissected and distinctly described; every one of which is essential to the performance of some one motion or other, which contributes to our ease and enjoyment; and, in most instances, a great number of them is required to perform their different functions at the same time. It has been calculated, that about a hundred muscles are employed every time we breathe.— “Breathing with ease,” says Dr. Paley, “is a blessing of every moment; yet, of all others, it is that which we possess with the least consciousness. A man in an asthma is the only man who knows how to estimate it.”

The Heart and Blood-vessels.—The heart is a hollow muscular organ, of a conical shape, and consists of four distinct cavities. The two largest are called ventricles, and the two smallest auricles. The ventricles send out the blood to the arteries; the auricles receive it from the veins. The heart is inclosed in the pericardium, a membranous bag, which contains a quantity of water or lymph. This water lubricates the heart, and facilitates all its motions. The heart is the general reservoir of the blood. When the heart contracts, the blood is propelled from the right ventricle into the lungs, through the pulmonary arteries, which like all the other arteries, are furnished with valves that play easily forward, but admit not the blood to return toward the heart. The blood, after circulating through the lungs, and having there been revivified by coming in contact with the air, and imbibing a portion of its oxygen, returns into the left auricle of the heart, by the pulmonary vein. At the same instant, the left ventricle drives the blood into the aorta, a large artery which sends off branches to supply the head and arms. Another large branch of the aorta descends along the inside of the backbone, and detaches numerous ramifications to nourish the bowels and inferior extremities. After serving the most remote extremities of the body, the arteries are converted into veins, which, in their return to the heart, gradually unite into larger branches, until the whole terminate in one great trunk, called the vena cava, which discharges itself into the right auricle of the heart, and completes the circulation. Each ventricle of the heart is reckoned to contain about one ounce, or two table spoonsful of blood. The heart contracts 4000 times every hour; and, consequently, there passes through it 250 pounds of blood in one hour. And if the mass of blood in a human body be reckoned at an average at twenty-five pounds, it will follow, that the whole mass of blood. passes through the heart, and consequently through the thousands of ramifications of the veins and arteries, ten times every hour, or about once every six minutes. We may acquire a rude idea of the force with which the blood is impelled from the heart, by considering the velocity with which water issues from a syringe, or from the pipe of a fire-engine. Could we behold these rapid motions incessantly going on within us, it would overpower our minds with astonishment, and even with terror. We should be apt to feel alarmed on making the smallest exertion, lest the parts of this delicate machine should be broken on-deranged, and its functions interrupted. The arteries into which the blood is forced, branch in every direction through the body, like the roots and branches of a tree; running through the substance of the bones, and every part of the animal frame, until they are lost in such fine tubes as to be wholly invisible. In the parts where the arteries are lost to the sight, the veins take their rise; and, in the commencement, are also imperceptible.

Respiration.—The organs of respiration are the lungs They are divided into five lobes; three of which lie on the right, and two on the left side of the thorax. The substance of the lungs is chiefly composed of infinite ramifications of the trachea, or windpipe, which, after gradually becoming more and more minute, terminate in little cells or vesicles, which have a free communication with one another. At each inspiration, these pipes and cells are filled with air, which is again discharged by expiration. In this manner, a circulation of air, which is necessary to the existence of men and other animals, is constantly kept up as long as life remains. The air-cells of the lungs open into the windpipe, by which they communicate with the external atmosphere. The whole internal structure of the lungs is lined by a transparent membrane, estimated at only the thousandth part of an inch in thickness; but whose surface from its various convolutions, measures fifteen square feet, which is equal to the external surface of the body. On this thin and extensive membrane innumerable veins and arteries are distributed, some of them finer than hairs; and through these vessels all the blood of the system is successively propelled, by a most curious and admirable mechanism. It has been computed that the lungs, on an average, contain about 280 cubic inches, or about five English quarts of air. At each inspiration, about forty cubic inches of air are received into the lungs, and the same quantity discharged at each expiration. On the supposition that twenty respirations take place in a minute, it will follow that, in one minute, we inhale 800 cubic inches; in an hour, 48,000; and in a day, one million one hundred and fifty-two thousand cubic inches—a quantity which would fill seventy-seven wine hogsheads, and would weigh fifty-three pounds Troy. By means of this function, a vast body of air is daily brought into contact with the mass of blood, and communicates to it its vivifying influence; and, therefore, it is of the utmost importance to health, that the air, of which we breathe so considerable a quantity, should be pure and uncontaminated with noxious effluvia.

In respiration, the air meets the blood in the lungs, and part of the oxygen of the atmosphere is absorbed by it, and imparts to it its red color. Part of the oxygen is also converted into carbonic acid by combining with carbon, or charcoal, in the lungs. In every instance, air which has been respired loses a part of its oxygen; the quantity varies at different times, according to the operation of certain external agents. It is reckoned that, upon an average, a man under ordinary circumstances consumes 45,000 cubic inches, or 15,500 grains of oxygen, in 24 hours. A quantity of carbonic acid is at the same time produced, which is generally somewhat less than the oxygen consumed, and may be reckoned at 40,000 cubic inches in 24 hours. It has been found that in the human species different individuals consume different quantities of oxygen, and of course return different quantities of carbonic acid. The breath expired has been shown to contain from 6 to 8 per page 111 cent, of carbonic acid It has been found that the nitrogen of the air inspired is sometimes returned in full volume, and sometimes is partially retained and disappears. On the whole, as respiration is one of the most important functions of animal life, on which our very existence depends, so we may plainly perceive, from the above and other circumstances, with what a variety of other functions it is connected, and on what a variety of minute and invisible processes its operations depend.

Digestion.—This process is performed by the stomach, which is a membranous and muscular bag, furnished with two orifices. By the one, it has a communication with a gullet, and by the other, with the bowels. The food, after being moistened by the saliva, is received into the stomach, where it is still further diluted by the gastric juice, which has the power of dissolving every kind of animal and vegetable substance. Part of it is afterward absorbed by the lymphatic and lacteal vessels, and carried into the circulating system, and converted into blood for supplying that nourishment which the perpetual waste of our bodies demands.

Perspiration is the evacuation of the juices of the body through the pores of the skin. It has been calculated that there are above three hundred thousand millions of pores in the glands of the skin which covers the body of a middle-sized man. Through these pores more than one-half of what we eat and drink passes off by insensible perspiration. If we consume eight pounds of food in a day, five pounds of it are insensibly discharged by perspiration. During a night of seven hours’ sleep, we perspire about forty ounces, or two pounds and a half. At an average, we may estimate the discharge from the surface of the body, by sensible and insensible perspiration, at from half an ounce to four ounces an hour. This is a most wonderful part of the animal economy, and is absolutely necessary to our health, and even to our very existence. When partially obstructed, colds, rheumatisms, fevers, and other inflammatory disorders, are produced; and were it completely obstructed, the vital functions would be clogged and impeded in their movements, and death would inevitably ensue.

Sensation.—The nerves are generally considered as the instruments of sensation. They are soft white cords which proceed from the brain and spinal marrow. They come forth originally by pairs. Ten pair proceed from the medullary substance of the brain, which are distributed to all parts of the head and neck. Thirty pair proceed from the spinal marrow, through the vertebrae, to all the other parts of the body; being forty in all. These nerves, the ramifications of which are infinitely various and minute, are distributed upon the heart, lungs, blood-vessels, bowels, and muscles, until they terminate on the skin or external covering of the body. Impressions of external objects are received by the brain from the adjacent organs of sense, and the brain exercises its commands over the muscles and limbs by means of the nerves.

Without prosecuting these imperfect descriptions further, I shall conclude this very hasty sketch with the following summary of the parts of the body, in the words of Bonnet.—“The bones, by their joints and solidity, form the foundation of this fine machine: the ligaments are strings which unite the parts together: the muscles are fleshy substances, which act as elastic springs to put them in motion: the nerves, which are dispersed over the whole body, connect all the parts together: the arteries and veins like rivulets, convey life and health throughout: the heart, placed in the center, is the focus where the blood collects, or the acting power by means of which it circulates and is preserved: the lungs, by means of another power draw in the external air, and expel hurtful vapors: the stomach and intestines are the magazines where everything that is required for the daily supply is prepared: the brain, that seat of the soul, is formed in a manner suitable to the dignity of its inhabitant: the senses, which are the soul's ministers, warn it of all that is necessary either for its pleasure or use.^* Adorable Creator! with what wonderful art hast thou formed us! Though the heavens did not exist to proclaim thy glory—though there were no created being upon earth but myself, my own body might suffice to convince me that thou art a God of unlimited power and infinite goodness.”

This subject suggests a variety of moral and religious reflections, but the limits to which I am confined will permit me to state only the following:—

1.

The economy of the human frame, when seriously contemplated, has a tendency to excite admiration and astonishment, and to impress us with a sense of our continual dependence on a Superior Power. What an immense multiplicity of machinery must be in action, to enable us to breathe, to feel, and to walk! Hundreds of bones of diversified forms, connected together by various modes of articulation; hundreds of muscles to produce motion, each of them acting in at least ten different capacities (see p. 36); hundreds of tendons and ligaments to connect the bones and muscles; hundreds of arteries to convey the blood to the remotest part of the system; hundreds of veins to bring it back to its reservoir the heart; thousands of glands secreting humors of various kinds from the blood; thousands of lacteal and lymphatic tubes, absorbing and conveying nutriment to the circulating fluid; millions of pores, through which the perspiration is continually issuing; an infinity of ramifications of nerves, diffusing sensation throughout all the parts of this exquisite machine; and the heart at every pulsation exerting a force of a hundred thousand pounds, in order to preserve all this complicated machinery in constant operation! The whole of this vast system of mechanism must be in action before we can walk across our apartments! We admire the operation of a steam-engine, and the force it exerts. But, though it is constructed of the hardest materials which the mines can supply, in a few months, some of its essential parts are worn and deranged, even although its action should be frequently discontinued. But the animal machine, though constructed, for the most part, of the softest and most flabby substances, can go on without intermission in all its diversified movements, by night and by day, for the space of eighty or a hundred years! the heart giving ninety-six thousand strokes every twenty-four hours, and the whole mass of blood rushing through a thousand pipes of all sizes every four minutes! And is it man that governs these nice and complicated movements? Did he set the heart in motion, or indue it with the muscular force it exerts? And when it has ceased to beat, can he command it again to resume its functions? Man knows neither the secret springs of the machinery within him, nor the half of the purposes for which they serve, or of the movements they perform. Can anything more strikingly page 112 demonstrate our dependence every moment on a Superior Agent, and that it is “in God we live and move and have our being?” Were a single pin of the machinery within us, and over which we have no control, either broken or deranged, a thousand movements might instantly be interrupted, and our bodies left to crumble into the dust.

It was considerations of this kind that led the celebrated physician Galen, who was a skeptic in his youth, publicly to acknowledge that a Supreme Intelligence must have operated in ordaining the laws by which living beings are constructed. And he wrote his excellent treatise, “On the uses of the parts of the human frame,” as a solemn hymn to the Creator of the world. “I first endeavor from His works,” he says, “to know myself, and afterward by the same means to show him to others; to inform them how great is his wisdom, his goodness, his power.” The late Dr. Hunter has observed, that Astronomy and Anatomy are the studies which present us with the most striking view of the two most wonderful attributes of the Supreme Being. The first of these fills the mind with the idea of his immensity, in the largeness, distances, and number of the heavenly bodies; the last astonishes us with his intelligence and art, in the variety and delicacy of animal mechanism.

2.

The study of the animal economy has a powerful tendency to excite emotions of gratitude. Man is naturally a thoughtless and ungrateful creature. These dispositions are partly owing to ignorance of the wonders of the human frame, and of the admirable economy of the visible world; and this ignorance is owing to the want of those specific instructions which ought to be communicated by parents and teachers, in connection with religion. For there is no rational being, who is acquainted with the structure of his animal system, and reflects upon it with the least degree of attention, but must feel a sentiment of admiration and gratitude. The science which unfolds to us the economy of our bodies, shows us, on what an infinity of springs and motions and adaptations, our life and comfort depend. And when we consider, that all these movements are performed without the least care or laborious effort on our part, if we be not altogether brutish, and insensible of our dependence on a Superior Power, we must be filled with emotions of gratitude toward Him “whose hands have made and fashioned us, and who giveth us life, and breath, and all things.” Some of the motions to which I have adverted depend upon our will; and with what celerity do they obey its commands? Before we can rise from our chair, and walk across our apartment, a hundred muscles must be set in motion; every one of these must be relaxed or constricted, just to a certain degree, and no more; and all must act harmoniously at the same instant of time; and at the command of the soul, all these movements are instantaneously performed. When I wish to lift my hand to my head, every part of the body requisite to produce the effect is put in motion: the nerves are braced, the muscles are stretched or relaxed, the bones play in their sockets, and the whole animal machine concurs in the action, as if every nerve and muscle had heard a sovereign and resistless call. When I wish, the next moment, to extend my hand to my foot, all these muscles are thrown into a different state, and a new set are brought along with them into action; and thus we may vary, every moment, the movements of the muscular system, and the mechanical actions it produces, by a simple change in our volition. Were we not daily accustomed to such varied and voluntary movements, or could we contemplate them in any other machine, we should be lost in wonder and astonishment.

Beside these voluntary motions, there are a thousand important functions which have no dependence upon our will. Whether we think of it or not, whether we be sleeping or waking, sitting or walking—the heart is incessantly exerting its muscular power at the center of the system, and sending off streams of blood through hundreds of pipes; the lungs are continually expanding and contracting their thousands of vesicles, and imbibing the vital principle of the air; the stomach is grinding the food; the lacteals and lymphatics are extracting nourishment for the blood; the liver and kidneys drawing off their secretions; and the perspiration issuing from millions of pores. These, and many other important functions with which we are unacquainted, and over which we have no control, ought to be regarded as the immediate agency of the Deity within us, and should excite our incessant admiration and praise.

There is one peculiarity in the constitution of our animal system, which we are apt to overlook, and for which we are never sufficiently grateful; and that is, the power it possesses of self-restoration. A wound heals up of itself; a broken bone is made firm again by a callus; and a dead part is separated and thrown off. If all the wounds we have ever received were still open and bleeding afresh, to what a miserable condition should we be reduced? But by a system of internal powers, beyond all human comprehension as to the mode of their operation, such dismal effects are effectually prevented. In short, when we consider, that health depends upon such a numerous assemblage of moving organs, and that a single spring out of action might derange the whole machine, and put a stop to all its complicated movements, can we refrain from joining with the Psalmist in his pious exclamation, and grateful resolution, “How precious are thy wonderful contrivances concerning me, O God! how great is the sum of them! I will praise thee; for I am fearfully and wonderfully made. Marvelous are thy works, and that my soul knoweth right well.”

Omitting the consideration of several other departments of science, I shall, in the meantime, notice only another subject connected with religion, and that is