This section is from the book "Human Physiology For The Use Of Elementary Schools", by Charles Alfred Lee. Also available from Amazon: Human Physiology, for the Use of Elementary Schools.
9. In like manner is the heart affected by the exciting and depressing passions. It throbs irregularly under the influence of fear and terror; it beats high and strong under the influence of joy; while its action is weakened under the operation of grief and care; in short, it is affected in a greater or less degree by every emotion which agitates the human breast. But this no more proves that the passions are seated in the heart, than that they are seated in the eye, because grief brings tears into that organ. Neither has the liver, as the ancients believed, any relation to the passions of rage and vexation, although a fit of jaundice, may, in some persons labouring under a disease of this organ, follow a paroxysm of these passions. In other individuals, a fit of dyspepsia may follow as a consequence of the same emotions ; or any other organ, may suffer, according as it is predisposed by debility, disease, or other causes. Such phenomena only prove that the whole body is bound up in one indissoluble bond of sympathy, or as St. Paul expresses it, " God hath tempered the body together, that there should be no schism in the body, but that the members should have the same care one for another ; so that, whether one member suffer, all the members suffer with it, or one member be honored, all the members rejoice with it."
10. The brain, like all the other organs of the body, increases in volume, by the exercise of its functions. When the mind is properly cultivated, the brain attains its full growth and development; and where suitable opportunities of education have been enjoyed, the intellectual powers are generally proportioned to the size of this organ. Majendi says, " The volume of the brain is generally in direct proportion to the capacity of the mind." This was also believed by the ancient Greeks ; for their statuaries, or workers in marble, made the heads of their Apollo, and other intellectual gods and heroes, much larger than the heads of their Hercules, and other heroes, who were remarkable only for their great physical strength. The heads of idiots are known to be extremely small; some, indeed, are not more than one fifth the average size.
11. That the brain is constructed with evident design, and is composed of a number of curiously wrought parts, all physiologists admit; yet they have not been able thoroughly to penetrate the intention with which they are formed, or to agree with respect to the particular functions which each part performs. It is, however, pretty well ascertained, that the hemispheres of the large brain, or cerebral lobes, are the instruments by which the intellectual operations are carried on ; in other words, are the seats of the faculties of thinking, memory, and the will; while the central parts, such as the optic lobes, and the medulla oblongata, are principally concerned in sensation ; and that the cerebellum, or little brain, is the chief sensorial agent in voluntary motion, and the seat of the animal, or lower propensities.
12. Many cruel experiments have been made on living animals, to determine the exact functions of particular parts of the brain ; but so much violence is done in these experiments, that but little dependence can be placed on them. Many attempts have been made to determine the exact place in the brain where perception resides, but all such attempts have been fruitless. That it is placed in the base of the brain, or the medulla oblongata, is very probable, as most of the nerves of sense terminate in that part; but it is difficult to prove this by actual experiment.
13. The brain, like all the organs of the senses, is double; the one side, as in the eyes, ears, and limbs, being exactly similar to the other ; so that it may be said, that we have two brains as well as two optic nerves, and two eyes. As the structure of the brain is fibrous, in order that the two sets of fibres may co operate, and constitute a single organ, they pass obliquely across from one side of the brain to the other, and these bridges constitute what are called the commissures of the brain. It follows from this, that if the right side of the brain receives an injury, it will be felt on the opposite side of the body. The following case proves this.
14. A piece of wire pierced the brain of a boy just over the right eye ; he immediately lost all motion in the left arm and leg, although his sense of feeling was as perfect as ever. There are many such cases on record, which conclusively show that the right side of the brain furnishes nerves of sense and motion to the left side of the body ; and the left side of the brain to the right side of the body. If, then, a portion of brain is lost by a wound, on one side of the head only, as has often happened, and the intellect does not suffer ; as the brain is a double organ, it does not prove, that it is not the seat of the mental faculties.
15. The office of the cerebellum is supposed by many to be, to regulate and combine different motions. For example, if the cerebellum be wounded, the animal cannot walk without staggering, and there will be a particular weakness on that side which is wounded. When a person is intoxicated, his inability of walking in a straight course, is supposed to be owing to the influence of the alcohol on the cerebellum. In experiments, where the cerebellum has been wounded or divided, the animal has rolled over and over, or whirled round and round ; the eyes squinted ; and all power of regulating its motions seems to have been lost.
16. Though man is infinitely exalted above the brute creation, by the endowments of reason and a moral sense, yet many of the inferior animals excel him in the perfection of subordinate powers. In strength and swiftness, he is surpassed by many of the quadrupeds ; in powers of vision, the eagle and other birds excel him ; in acuteness of hearing, taste, and smell, a large number of animals are superior to him. Man is indeed a stranger to those delicate perceptions, which teach the lower animals to seek the food which is salutary, and avoid that which is injurious, and has to depend upon a painful and hazardous experience for that knowledge which the brutes possess by instinct.