Thought and will. Instinctive and automatic motions. This is accomplished in both in substantially the same way. The means by which it is done, and its arrangements are modified, as you have seen, in the two cases, to suit the differing circumstances. The nervous system, observe, then, is, for particular purposes, superadded in the animal to what is common both to the animal and the plant, and so constitutes the essential difference between them. And so, all the functions relating to nutrition, which are of course common to plants and animals, are called functions of organic life. But the functions which are performed by the system superadded in the animal, the chief of which are sensation and spontaneous motion, are termed functions of animal life. These are sometimes also called functions of relation, from the especial connection which they form between the animal and all that is around him. 33. These animal functions, sensation and spontaneous motion, imply thought and will. The order of action is this: sensation-thought in regard to it-action of the will in consequence of thought then, from this action, an impression carried through nerves to organs termed muscles-motion in them from their contraction. This order, however, is not always observed. The first link, sensation, may be absent. Thought, without any preceding sensation, may prompt the will, and spontaneous motion results. The action of the will, too, may be left out, or may be in opposition. Thus, emotions may produce action of the muscles, the will not concurring, and perhaps opposing; as when we laugh at what is ridiculous, or weep at what is sad, in spite of restraining efforts dictated by the will. 34. There are also instinctive motions, and motions which are termed automatic, with which the will has no direct connection. And the connection of sensation with them is, in some cases at least, doubtful. The action of the muscles, in swallowing, breathing, &c., and the action of that compound muscle, the heart, are examples of motions more or less disconnected from the will, and also from sensation. The action of the heart is wholly removed from the direct influence of the will, and it is at least not obvious that it is influenced directly by sensation. It is influenced indirectly by both, through the agency of emotions awakened by them. The muscles of breathing, on the other hand, though ordinarily involuntary, may be directly influenced both by the will and by sensation. You can at will breathe faster and more deeply, and sensations of uneasiness in the chest modify the breathing. Central organs of nervous system. Most developed in man. 35. For all these different actions, thus produced in different ways, there are central parts of the nervous system upon which the causes of these actions produce the impressions or impulses from which the actions result. Thus, when a sensation is followed by a spontaneous action of muscles, an impression is conveyed by nerves to the central organ; the will there acts, and the impulse there given by this action of the will is carried by other nerves to the muscles, which execute the intended movement. 36. These central parts or organs, which are the media, the instruments of impressions, are in different parts of the body of the animal; but the most important of them is what we call the brain. This part is developed most in those animals that give the greatest evidences of intelligence; and, therefore, it is more prominent in man than in any other animal. 37. It may be remarked, as a general truth, that the nervous system, and its associate or subordinate system, the muscular, are developed in different degrees or forms, to suit the different characters and wants of animals. In man, they are more complex and perfect than in any other animal. The brain, in him, is a large organ, occupying the skull. The spinal marrow, and other central parts, and the nerves, are largely developed. And the muscles which are moved by this nervous system form a large portion of the bulk of the body. The organs of nutrition, analogous to those which make up nearly the whole of the plant, occupy the two cavities of the trunk of the body, the thoracic and the abdominal. But, as we descend in the animal kingdom, the nervous system becomes continually less prominent, and the system of mere nutrition more so. We at length come to animals, in which the nervous system is a mere small appendage to the system of nutrition, and only serves to direct the muscles in securing the food of the animal. In some of these, we not only do not find a brain, but we fail to discover any traces of a nervous system. This is true of the Hydra, noticed in § 29. 38. The nervous system, which so clearly distinguishes most animals from all plants, is fairly presumed to exist, though in an exceedingly slight degree, in those beings in which it can not be found, but in which we find other characteristics of the animal kingdom. And it is presumed, also, that the exercise of thought and the action of the will, which most animals so plainly exhibit, while they become less and less obvious as we descend in the scale, are not wholly obliterated in the very No nervous system in some animals; yet feeling and thought. lowest animals. It may, perhaps, be said, that as muscular action, as mentioned in § 34, is sometimes produced even in man without the intervention of thought or the will, it may be produced in animals of the lowest order altogether in this way. But we may more rationally infer that, as the chief object of motion in them is the securing of food, it is guided by the action of a will in obedience to their sensations. In other words, it is truly a spontaneous, and not a mere automatic motion. And it is probable that there is in the very lowest of animals some degree, though it may indeed be slight, of enjoyment in the sensations received from the moving water about it, and from the satisfying of its wants in the process of nutrition. We will take the Hydra, a representation of which is given in Fig. 1, page 23, as an illustration of the above remarks. It is a minute gelatinous animal, in which no nervous or muscular fibres can be found. And yet it has an extraordinary power of extending and contracting itself. When it is alarmed, it draws in its arms, and shrinks into the form of a little globule; and if you should see it in this condition, you would not suspect that it had any arms or tentacula. But when it is searching for food, it often extends its body and its arms to a great length; and when it grasps its prey, it puts it into its stomach, which constitutes, so far as we can see, its whole body. We can not conceive of all these motions, thus executed to effect certain definite objects, without the agency of a will, and without sensations to prompt the will and guide the motions. The animal must have a power of choice, or it would put a bit of stick or straw into its stomach as readily as a worm or an insect. But the tentacula never grasp, among the various bits of things which float against them, any thing beside the appropriate food of the animal. And it undoubtedly enjoys its food as really, though perhaps not as vividly, as any human epicure; and has in some measure the same pleasurable sensations which locomotion produces in us, as it floats along so quietly, with its arms hanging down from its body. Though there be no nervous fibres to be seen in the loose gelatinous structure of this little creature, yet, as the phenomena which it exhibits are known to be produced by the nervous system in those animals whose structure is more plainly and thoroughly developed, we justly infer that there must be nervous matter, in some form, in this and other similar animals. 39. One more important distinction between animals and Peculiar endowments of man. Abstract reasoning. Conscience. plants remains to be noticed. It relates to their chemical composition. I stated, in § 23, that organized substances are composed mostly of four elements-oxygen, hydrogen, nitrogen, and carbon. Plants differ from animals, in having but little nitrogen in their composition. It was formerly supposed that they contained none of this element. It is found only in particular parts of plants, as the seeds. We may regard carbon as the most characteristic constituent of vegetables, and nitrogen of animals. And in this connection it is interesting to observe that, while carbon is largely thrown off from the lungs of animals, in the shape of carbonic-acid gas, it is as largely absorbed by the leaves of plants. Of this fact I shall take more particular notice when I come to the subject of respiration. CHAPTER III. MAN IN HIS RELATIONS TO THE THREE KINGDOMS OF NATURE. 40. MAN is commonly spoken of as being at the head of the animal kingdom, and in the book of the naturalist is made an order of the class termed Mammalia. As the basis of the whole classification is mere material organization, and has no reference at all to mental or spiritual endowments, the classification, in regard to man, is in its principle correct. At the same time, it must be admitted, that it fails to recognize altogether the essential distinctions between man and other animals. These distinctions, making, as they do, a wide gap-"an impassable chasm," as Professor Guyot expresses it-between man and the inferior animals, are to be found in certain peculiar spiritual endowments which man possesses. These I will notice now in the briefest manner, leaving it for another part of this book to treat more fully of this and other kindred subjects. One of these endowments is the power of abstract reasoning. Other animals in a certain sense reason, that is, they make inferences; but they never arrive at any general or abstract truths. Another endowment is a moral one, linking man in his spiritual nature to the Deity. It is conscience, or the knowledge and sense of what is right, in distinction from what is wrong. Other animals, in obedience to the passions of fear and love, Immortality. Real relation to the animal kingdom. sometimes appear to the superficial observer to have an idea of what is right, as such; but there is not the slightest evidence that they really have any such knowledge. 41. In view of these endowments of man, it is wrong to consider him merely as being at the head of the animal kingdom. He is something more than this. He is so much and so distinctly more, that the accepted classification of him, on the ground of mere difference of organization, gives a most inadequate idea of his true position in the scale of being. It leaves entirely out of view the essential distinctions; and it separates man from other animals, as you will see, by a distinction of organization which is of rather a trivial, perhaps questionable, character. 42. The force of this view of the subject is enhanced, if we take into consideration that great fact, revealed to us by God in his Word, that man is destined to immortality. It may be objected that, as this fact is learned only by revelation, and not by observation, it is not to be regarded as a scientific fact. But, granting that there is truth in the objection, it certainly is allowable to allude to the revelations of Scripture, as confirming or enforcing views developed by scientific observation. This is all that I have done in this case. The view which I have presented is based upon endowments that are recognized by the scientific observer, without the aid of revelation; and I appeal to the revealed fact of man's immortality, as adding force to this view, and not as being at all necessary to the establishment of its truth. 43. Let us look at this subject in another point of view. The grand essential distinction between animals and plants lies, as you have seen in the last chapter, in the fact that animals have a nervous system. Now, with this system, as you have also seen, appear certain mental manifestations. These differ widely in different animals, and are most prominent in those in which this system is most prominent and complicated. As we trace upward these complications, when we come to man, we find certain mental manifestations, which separate him by "an impassable chasm" from all other animals. Till we arrive at him, the difference is one of degree, for the most part. But in his case it is a difference of kind, and a very wide one. Of such a difference the naturalist should certainly take very distinct cognizance; and, if it be not consistent for him to do so in his classification, great force and prominence should be given to these views in his instructions on this subject. As the super |