صور الصفحة
PDF
النشر الإلكتروني

less vain and absurd than it would confessedly be to attempt to handle electricity and gravitation as forces apart from the changes in matter by which alone we know them. As there are different kinds of matter, so there are different modes of force, in the universe; and as we rise from the common physical matter in which physical laws hold sway up to chemical matter and chemical forces, and from chemical matter again up to living matter and its modes of force, so do we rise in the scale of life from the lowest kind of living matter, with its corresponding force or energy, through different kinds of histological elements, with their corresponding energies or functions, up to the highest kind of living matter and corresponding mode of force with which we are acquainted, viz. nerve element and nerve force. But, when we have arrived at nerve element and nerve force, it behoves us not to rest content with the general idea, but to bestow pains on the patient and careful discrimination of the different kinds of nerve-cells in the nervous system, and to study their different manifestations of energy. So only shall we obtain the groundwork of a true conception of the relations of mind and the nervous system.

The chief feature to be noted in this upward transformation of matter and correlative metamorphosis of force is, that the exaltation or transpeciation on each occasion represents an increased speciality of elements, and a greater complexity of combinations, in a smaller space : all exaltation of matter and force is, as it were, a concentration thereof. As one equivalent of chentical force corresponds to several equivalents of inferior force, and one equivalent of vital force to several equivalents of chemical force; so in the scale of tissues the higher kind represents a more complex elementary constitution, and a greater number of simultaneously acting forces, than the kind of tissue below it in dignity. If we suppose a higher tissue to undergo decomposition, or ritrograde metamorphosis of its matter, with which must necess.crily coincide a resolution of its (nergy into lower modes, then we might say that a single mnad of the higher tissue, or one equivalent of its force, would equal in value several monads of the lower kind of tissue, or several «quivalents of its force. The characteristic of living matter is the complexity of combinatious and the variety of elements in so small

a compass that we cannot yet trace them; and in nerve structure this complication and concentration is carried to its highest pitch. Nervous tissue with its energy is, therefore, dependent for its existence on all the lower kinds of tissue that have preceded it in the order of development: all the force of nature could not develop a nerve-cell directly out of inorganic niatter. The highest energy in nature is really the most dependent; in the fact that it is so dependent, that it implicitly contains the essence or abstraction of all the lower kinds of energy, lies the reason of the powerful influence which it is able to exercise over all the lower forces that are subservient to its evolution. As the man of genius implicitly contains humanity, so nerve element implicitly contains nature.*

What is the progress or nisus that is manifest on surveying nature as a whole ? Is it not the struggle to arrive at consciousness, to attain to self-communion? In the series of her manifold productions man was, so to speak, says Goethe, the first dialogue that Nature held with God. Every poet, then, who is sensitive to a hitherto unrevealed subtlety of human feeling, every philosopher who apprehends and reveals a hitherto unobserveil relation in nature, is, each in his place, aiding the onward progress; in his art nature is underoing evolution; in him the world is, more or less, rugencrale.

"To whom the winge. I hierarch rrpolied :-
O Adam, onc Almighty is, from whom
All things primreil, and up to Him return,
If not depraved from good, created all
Such to perfertion, one first matter all,
Indued with various forins, various degrees
Of substance, and in things that liv, of life ;
But more refined, more spirituous, and pure,
As nearer to Himn placed, or nearer tending,
Fach in their - veral active spheres assigned,
Till body up to spirit work, in bouwils
Proportioned ' each kind. So from the root
Springs lighter the green stalk, from thence tho leaves

• For the further derely cent of this view of life, I may refer to an articlo on the “ Theory of Vilali:.," in the British and Foreign Med. Ci.r. Review, . In tober 1863.

Moro aery, last the bright consummate flower
Spirits odórous breathes : flowers and their fruit,
Man's nourishment, by gradual scale sublimed,
To vital spirits aspire, to animal,
To intellectual; give both life and sense,
Fancy and understanding ; whence the soul
Reason receives, and reason is her ing,

Discursive, or intuitive ; discourse
: Is oftest yours, the latter most is ours,
Differing but in degree, of kind the same.

Paradise Lost, P. v.

CHAPTER III.

TIIE SPINAL CORD, OR TERTIARY NERVOUS CENTRES; OR

NERVOUS CENTRES OF REFLEX ACTION.

OMITTING for the present any mention of the organic

nervous centres of the sympathetic system-first, because they minister chiefly to the organic life, and very little is definitely known about them; and, secondly, because something will be said of them incidentally when treating of the Passions -We go on to show forth the functions of the spinal cord. It is not a conducting organ only, but contains many independent nerve centres. A larve part of human activity notably takes place without any voluntary control, or even without any consciousness on the part of the individual; and of these unconscious or involuntary actions a great part is as plainly due to the independent power of reaction which the ganglionic cells of the spinal cord have. If it be cut across at a spot below where the respiratory nerves are given off, all sensation and motor power are lost in the parts of the body below the section. But is the sole of the foot be then tickled with a feather, the leg is drawn up, though the man is unaware of it unless inforined by others of what has happened. Such automatic action of the spinal cord, manifest enough in the actions of man, but still more so in those of the lower animals, may be illustrated both from the animal kingdom and from the phenomena of human life.

When the earliest a tions of the new-born infant are observed, it is plain that, like the movements of the fætus within the mother's womb, or the movements of many of the lower animais, they are simply refles to impressions, and take place without will, or even without consciousness. The anencephalic infant, in which absence of bruin involves an alsence of consciousness, not only exhibits move muculs of its limnls, but is capall. also of

the associated reflex acts of sucking and crying. A decapitated frog, to the thigh of which acetic acid has been applied, makes certain movements for the purpose of wiping off the acid; and if the head of a frog, which is clinging to the female at the season of copulation, be cut off, the animal still holds her fast; nay, if its paw be afterwards cut off, clings to her with its bloody stump. The spinal cord is plainly, then, not only a centre of irregular reflex movements, but it is also a centre of co-ordinate or so-called designed actions. Pflüger wetted with acetic acid the thigh of a decapitated frog over its internal condyle; it wiped it off with the dorsal surface of the foot of the same side: he thereupon cut off the foot, and applied the acid to the same spot; the animal, as though it were deceived, as the man who has lost a limb at first is, by an eccentric sensation, would have wiped it off again with the foot of that side, but of course could not. After some fruitless efforts, therefore, it ceased to try in that way, seemed unquiet, "as though it were searching for some new means," and at last it either made use of the foot of the leg which was left, or it so bent the mutilated limb that it succeeded in wiping it against the side of its body. So much was Pfüger impressed by this wonderful adaptation of means to an end in a headless animal, that he actually inferred that the spinal cord, like the brain, was possessed of sensorial functions. Others, who would scarce admit the supposition to be true of man, have thought that it might be so of some of the lower animals. Instead of rightly grounding their judgment of the complex phenomena in man on their experience of the simpler instances exhibited by the lower animals, they applied to the lower animals their subjective misinterpretation of the complex phenomena in man.(')

It is obviously quite possible to draw another inference from Pflüger's experiment: that the so-called design of an act does not necessarily witness to the coexistence of will, forethought, or consciousness; that actions " having the semblance of predesigning consciousness" may, nevertheless, be unattended with consciousness.* No doubt there is a definite purpose in the

• Very interesting, in relation to this matter, are Prochaska's observations, published in 1781:-" Cum itaque precipua functio sensorii communis consi-zat in reflexionc impressionum sensoriorum in motorias, notandam est quod vla refierin rel animi inscid rel vero onimd conscid fat." Ho gives numer.1118 examples often given since by other authors, and adds :-"Omnes istæ actiones

« السابقةمتابعة »