Secondly, it is most needful, in order to avoid confusion, to apprehend the exact signification of what is understood by mind, according to the common and vague use of the word. It is really a general term acquired by observation of and abstraction from the manifold variety of mental phenomena: by such observation of the particular phenomena and appropriate abstraction from them we get, as an ultimate generalization, the general conception, or the, so to speak, essential idea, of mind. An illustration will help to exhibit what we mean. The steamengine is a complicated mechanism, of the construction and mode of action of which many people know very little, but it has a very definite function of which those who know nothing of its construction can still form a sufficiently distinct conception; the co-ordinate, integral action of the steam-engine, as we conceive it, is different from the nicely-adjusted mechanism or from the action of any part of it. But the function of the engine is dependent on the mechanism and on the co-ordinate action of its parts, cannot be dissociated from these, and has no real existence apart froin them, though it may exist separately as a conception in our minds. By observation of the mechanism and appropriate abstraction we get the essential idea of the steam-engine,—a fundamental idea of it, which, as our ultimate generalization, expresses its very nature as such, containing, as Coleridge would have said, "the inmost principles of its possibility as a steam-engine." So likewise with regard to the manifold phenomena of mind; by observation of them and abstraction from the particular we get the general conception or the essential idea of mind, an idea which has no more existence out of the mind than any other abstract idea or general term. In virtue, however, of that powerful tendency in the human mind to make the reality conformable to the idea, a tendency which has been at the bottom of so much confusion in philosophy, this general conception has been converted into an objective entity, and allowed to tyrannize over the understanding. A metaphysical abstraction has been made into a spiritual entity, and a complete barrier thereby interposed in the way of positive investigation. Whatever be the real nature of mind-and of that there is no need to speak here-it is most certainly dependent for its every manifestation on the brain

and nervous system; and now that scientific research is daily disclosing more clearly the relations between it and its organ, it is plainly most desirable to guard against the common metaphysical conception of mind, by recognising the true subjective character of the conception and the mode of its origin and growth.

A third important consideration is, that mental power is truly an organized result, not, strictly speaking, built up, but matured by insensible degrees in the course of life. The brain is not, like the liver, the heart and other internal organs, capable from the time of birth of all the functions which it ever discharges; for while, in common with them, it has a certain organic function to which it is born equal, its high special character in man as the organ of conscious life, the supreme instrument of his relations with the rest of nature, is developed only by a long and patient education. Though the brain, then, is formed during embryonic life, its highest development only takes place after birth; and, as will hereafter appear, the same gradual progress from the general to the special, which is exhibited in the development of the organ, is witnessed in the development of our intelligence. How inexact and misleading in this regard, therefore, is any comparison between it and the liver!

Nevertheless, it must be distinctly laid down, that mental action is as surely dependent on the nervous structure as the function of the liver confessedly is on the hepatic structure: that is the fundamental principle upon which the fabric of a mental science must rest. The countless thousands of nervecells which form so great a part of the delicate structure of the brain, are undoubtedly the centres of its functional activity: we know right well from experiment, that the ganglionic nervecells scattered through the tissues of organs, as for example through the walls of the intestines or the structure of the heart, are centres of nerve force ministering to their organic action; and we may confidently infer that the ganglionic cells of the brain, which are not similarly amenable to observation and experi ment, have a like function. Certainly they are not inexhaustible centres of self-generating force; they give out no more than what they have in one way or another taken in; they receive

material from the blood, which they assimilate, or make of the same kind with themselves; a correlative metamorphosis of force necessarily accompanying this upward transformation of matter, and the nerve-cell thus becoming, so long as its equilibrium is preserved, a centre of statical power of the highest vital quality. The maintenance of the equilibrium of nerve element is the condition of latent thought-it is mind statical; the manifestation of thought involves the change or destruction of nerve element. The nerve-cell of the brain, it might in fact be said, represents statical thought, while thought represents dynamical nerve-cell, or, more properly, the energy of

nerve-cell

So far from discussing whether mind is the function of the brain, the business which science now has immediately before it is the more special investigation of the conditions of activity of the ganglionic nerve-cell or groups of nerve-cells. If we look to those humbler animals in which nervous tissue makes its first appearance, it is plain that the simple mode of its existence in them allows of no other manner of proceeding; if we trace upwards the gradual increasing complication of the nervous system through the animal kingdom, it is evident that such manner of proceeding is the only one to furnish the materials of a comprehensive and sound induction; and if we duly weigh the results of physiological experiment and pathological research, it is no less certain that we must discard scientific investigation altogether in cerebral physiology, if we reject the ganglionic nerve-cell of the brain as a centre of mental force.

In the lowest forms of animal life nerve does not exist: the Protozoa aud many of the Zoophytes are destitute of any trace of nervous system. The most simple beings consist of a uniform, homogeneous substance, by means of which all their functions are executed. They are nouri-hed without digestive organs; breathe without respiratory ons; feel and move without organs of sense, without muscles, without nervous system. The stimulus which the little creature receives from without produces some change in the lecular relations of its almost homogeneous substance, and the insensible movements would seem to amount collectively to the sensible movement which it

makes; the molecular process in such case being not unlike that which takes place and issues in the coagulation of the blood, when the fibrine is brought in contact, as some think, with a foreign substance.* The perception of the stimulus by the creature is the molecular change which ensues, the imperceptible motion passing, by reason of the homogeneity of its substance, with the greatest ease from element to element of the same kind, as it were by an infection, or as happens in the sensitive plant; and the sum of the molecular motions, as necessarily determined in direction by the form of the animal, or by some not yet recognised cause, results in the visible movement. The recent researches of Graham into the colloidal condition of matter have proved the necessity of considerable modification in our usual conception of solid matter: instead of the notion of impenetrable, inert matter, we must substitute the idea of matter which, in its colloidal state, is penetrable, exhibits energy, and is widely susceptible to external agents, "its existence being a continued metastasis." This sort of energy is not a result of chemical action, for colloids are singularly inert in all ordinary chemical relations, but a result of its unknown intimate molecular constitution; and the undoubted existence of colloidal energy in organic substances which are usually considered inert and called dead, may well warrant the belief of its larger and more essential operation in organic matter, in the state of instability of composition in which it is when under the condition of life. Such energy would then suffice to account for the simple uniform movements of the homogeneous substance of which the lowest animal consists; and the absence of any differentiation of structure is a suflicient reason of the absence of any localization of function and of the general uniform reaction to different impressions. But it will be observed that even the movements of these simplest creatures, in which there is not the least indication of the elements of a nervous system, are not entirely vague, confused, and infinite; they present certain indications of adaptation to functional ends.

With the differentiation of tissue and increasing complexity

• Crooni in Lecture before the Royal Society, 1963. By Professor J. Lister, F.R.S. + Philosophical Transactions, 1862.

of organization, which are met with as we ascend in the animal kingdom, the nervous tissue appears, but at first under a very simple form. Its simplest type may be represented as two fibres that are connected by a nerve-cell or a ganglionic group of nervecells; the fibres are apparently simple conductors, and might be roughly compared to the conducting wires of a telegraph, while the cell, being the centre in which nerve force is generated, may be compared to the telegraphic apparatus; in it the effect which the stimulus of the afferent or centripetal nerve excites, is transmitted along the efferent or centrifugal nerve, and therein is displayed the simplest form of that reflex action which plays so large a part in animal life. This type of structure is repeated through the complex nervous system of all the higher animals. Cut across the afferent nerve, or otherwise interrupt its continuity, the impression cannot reach the centre; cut across the efferent nerve, the central excitation is powerless to influence the muscles or parts to which it is distributed. Not all the passion and eloquence of a Demosthenes could force its way outwards into words, if the motor nerves of the tongue were cut across. Owing to the differences of kinds of tissue, and to the specialization of organs in the more complex animal, there cannot plainly be that intimate molecular sympathy between all parts which there is in the homogeneous substance of the simplest monad; the easy motion, as by an infection, from particle to particle, is not possible in the heterogeneous body, where the elements are of a different kind accordingly special provision is required for insuring communication between different parts, and for co-ordinating and harmonizing the activity of different organs. The animal

• The fibres act as simple conluctors, and have like physiological properties. Philippeau and Vulpian (Comptes Rendus, vi.) and Rosenthal (Centralblatt, No. 29, 1864) have succeeded in uniting the central end of the cut lingual nerve, the sensory nerve of the tongue, with the peripheral end of the cut hypoglossal, the mot a nerve of the tongue. Stimulation of the central part of the lingual produced contractions of the tongue, such as norm dlly follow stimulation of the hypoglossil. Thus it is proved that the end of sensory nerve may be united with the end of a motor nerve, and when the union is complete, excitation of the sensory may be transmitted to the motor fibres. Inversely, stimulation of the peripher & end of the hypoglossal produced evide, ce of pain. It would wem that the cility is the same in all nerves; the difference of function being due, not to dif!nce of physiological properties, but to alference of connexion of the fibres. S also Legons sur la Physiologie Générale, ' comparée du Système Nerreuz, par A. Vulpian. 1866.