How to Determine the Position of an Animal. 331

tion of mat

dergo no destruction. Chemically speaking, they are eternal. The duraAnd so, likewise, force never deteriorates or becomes lessened. ter and imperishabiliIt may assume new phases, but it is always intrinsically unim- ty of force. paired. The only changes it can exhibit are those of aspect and of distribution of aspect, as electricity, affinity, light, heat; of distribution, as when the diffused aggregate of many sunbeams is concentrated in one animal form.

It is but little that we know respecting the mutations and distribution of force in the universe. We cannot tell what becomes of that which has characterized animal life, though of its perpetuity we may be assured. It has no more been destroyed than the material particles of which such animals consist. They have been transmuted into new forms-it has taken on a new aspect. The sum total of matter in the world is invariable; so, likewise, is the sum total of force.

Averrhoes.

These conclusions resemble in many respects those of the Theory of philosophy of Averrhoes, but they are free from the heresy which led the Lateran Council, under Leo X., to condemn the doctrines of the great Spanish Mohammedan. The error of Averrhoes consisted in this, that he confounded what is here spoken of under the designation of force with the psychical principle, and falsely applied that which is true for animals to the case of man, who is to be considered as consisting of three essentially distinct parts,—a material body, upon which operate various physical forces, guided and controlled by an intelligent soul.

In the following paragraphs the distinction here made is brought into more striking relief.

mode of de

The station of any animal in the organic series may be de- Anatomical termined from the condition of its nervous system. To this termining position in observation man himself is not an exception. Indeed, just the animal views of his position in the world, of the nature of his intel- series. lect and mental operations, cannot be obtained except from the solid support afforded by Anatomy. The reader has doubtless remarked that, in the historical sketch of the later progress of Europe given in this book, I have not referred to metaphysics, or psychology, or mental philosophy. Cultivated as they The uselesshave been, it was not possible for them to yield any other metaphysi

ness of the

cal sciences.

Necessity of

resorting to

332

Criticism on Psychology and Metaphysics.

result than they did among the Greeks. A lever is no mechanical power unless it has a material point of support. It is only through the physical that the metaphysical can be discovered.

An exposition of the structure, the physical forces, and the Anatomy, intellectual operations of man must be founded on anatomy. and Physiology. We can only determine the methods of action from the study of the mechanism, and the right interpretation of that mechanism can only be ascertained from the construction of its parts, from observations of the manner in which they are developed, from comparisons with similar structures in other animals, not rejecting even the lowest, and from an investigation of their habits and peculiarities. Believing that, in the present state of science, doctrines in psychology, unless they are sustained by evidence derived from anatomy and physiology, are not to be relied on, I have not thought it necessary to devote much space to their introduction. They have not taken a part in the recent advances of humanity. They belong to an earlier social period, and are an anachronism in ours. I have referred to these points heretofore in my work on 'Physiology,' and perhaps shall be excused the following extract (p. 259):

Solution of

psychologi

cal questions.

Uncertainty of metaphysics.

"The study of this portion of the mechanism of man brings us therefore in contact with metaphysical science, and some of its fundamental dogmas we have to consider. Nearly all philosophers who have cultivated in recent times that branch of knowledge, have viewed with apprehension the rapid advances of physiology, foreseeing that it would attempt the final solution of problems which have exercised the ingenuity of the last twenty centuries. In this they are not mistaken. Certainly it is desirable that some new method should be introduced, which may give point and precision to whatever metaphysical truths exist, and enable us to distinguish, separate, and dismiss what are only vain and empty speculations.

"So far from philosophy being a forbidden domain to the physiologist, it may be asserted that the time has now come when no one is entitled to express an opinion in philosophy except he has first studied physiology. It has hitherto been

to the detriment of truth that these processes of positive investigation have been repudiated. If from the construction of the human brain we may demonstrate the existence of a soul, is not that a gain? for there are many who are open to arguments of this class on whom speculative reasoning or a mere dictum falls without any weight. Why should we cast aside the solid facts presented to us by material objects? In his communications throughout the universe with us, God ever materializes. He equally speaks to us through the thousand graceful organic forms scattered in profusion over the surface of the earth, and through the motions and appearances presented by the celestial orbs. Our noblest and clearest conceptions of His attributes have been obtained from these material things. I am persuaded that the only possible route to truth in mental philosophy is through a study of the nervous mechanism. The experience of 2500 years, and the writings of the great metaphysical intellects attest, with a melancholy emphasis, the vanity of all other means.

of the in-.

tion of

“Whatever may be said by speculative philosophers to the Necessity contrary, the advancement of metaphysics is through the study terpretaof physiology. What sort of a science would optics have been structure. among men who had purposely put out their own eyes? What would have been the progress of astronomy among those who disdained to look at the heavens? Yet such is the preposterous course followed by the so-called philosophers. They have given us imposing doctrines of the nature and attributes of the mind in absolute ignorance of its material substratum. Of the great authors who have thus succeeded one another in ephemeral celebrity, how many made themselves acquainted with the structure of the human brain? Doubtless some had been so unfortunate as never to see one! Yet that wonderful organ was the basis of all their speculations. In voluntarily isolating themselves from every solid fact which might serve to be a landmark to them, they may be truly said to have sailed upon a shoreless sea from which the fog never lifts. The only fact they teach us with certainty is, that they know nothing with certainty. It is the inherent difficulty of their method that it must lead to unsubstantial results. What is

Intellectual relations

334

Composition of the Nervous System.

not founded on a material substratum is necessarily a castle in the air."

Considering thus that scientific views of the nature of man of man de- can only be obtained from an examination of his nervous syspend on his nervous tem, and that the right interpretation of the manner of action of that system depends on the guiding light of comparative anatomy and physiology, I shall, in the following exposition, present the progress of discovery on those principles.

system.

The rudimentary

nervous

system is

In those low tribes of life which show the first indications of a nervous system, its operation is purely mechanical. An exautomatic. ternal impression, as a touch, made upon animals of that kind, is instantly answered to by a motion which they execute, and this without any manifestation of will or consciousness. The phenomenon is exactly of the same kind as in a machine, of which, if a given lever is touched, a motion is instantly produced.

Two elementary forms of nerve matter.

Structure of a nerve fibre.

Function

of a nerve

duction.

In any nervous system there are two portions anatomically distinct. They are-1st, the fibrous; 2nd, the vesicular. It may be desirable to describe briefly the construction and functions of each of these portions. Their conjoint action will then be intelligible.

1st. A nerve fibre consists essentially of a delicate thread— the axis filament, as it is called-enveloped in an oil-like substance, which coagulates or congeals after death. This, in its turn, is enclosed in a thin investing sheath or membranous tube. Many such fibres bound together constitute a nerve.

The function of such a nerve fibre is indisputably altogether fibre is con- of a physical kind, being the conveyance of influences from part to part. The axis filament is the line along which the translation occurs, the investing material being for the purpose of confining or insulating it, so as to prevent any lateral escape. Such a construction is the exact counterpart of many electrical contrivances, in which a metallic wire is coated over with sealing-wax or wrapped round with silk, the current being thus compelled to move in the wire without any lateral escape. Of such fibres, some convey their influences to the interior, and hence are called centripetal; some convey them to the exterior, and hence are called centrifugal. No anatomical differ

ence in the structure of the two has, however, thus far been discovered. As in a conducting wire the electrical current moves in a progressive manner with a definite velocity, so in a nerve filament the influence advances progressively at a rate said to be dependent on the temperature of the animal examined. It seems in the cold-blooded to be much slower than in the hot. It has been estimated in the frog at eighty-five feet in a second; in man, at two hundred feet,—an estimate probably too low.

The fibres thus described are of the kind designated by physiologists as the cerebro-spinal; there are others, passing under the name of the sympathetic, characterized by not possessing the investing medullary substance. In colour they are yellowish-grey; but it is not necessary here to consider them further.

of a nerve

2nd. The other portion of the nervous structure is the vesi- Structure cular. As its name imports, it consists of vesicles filled with vesicle. a grey granular material. Each vesicle has a thickened spot or nucleus upon it, and appears to be connected with one or more fibres. If the connection is only with one, the vesicle is called unipolar; if with two, bipolar; if with many, multipolar or stellate. Every vesicle is abundantly supplied with blood.

of a nerve

As might be inferred from its structure, the vesicle differs Function altogether from the fibre in function. I may refer to page vesicle. 268 of my Physiology' for the reasons which have led to the inference that these are contrivances for the purposes of permitting influences that have been translated along or confined within the fibre to escape and diffuse themselves in the grey granular material. They also permit influences that are coming through many different channels into a multipolar vesicle to communicate or mix with one another, and combine to produce new results. Moreover, in them influences may be long preserved, and thus they become magazines of force. Combined together, they constitute ganglia or nerve-centres, on which, if impressions be made, they do not necessarily forthwith die out, but may remain gradually declining away for a long time. Thus is introduced into the nervous mechanism the element of