ergetory and sympathetic influence of the nervous system upon the different vital and natural functions, -these, though occurring simultaneously or successively in the same general economy, are all distinct operations, produced by organs specially destined for their performance, and depending partly on physical and chemical properties common to all kinds of matter; partly on vital properties peculiar to animal structures; and partly, also, on the mysterious connexion which subsists between the mind and its corporeal organs.

Nothing, certainly, could be more remote from the proper spirit of philosophical inquiry, than to refer, as Dr Brown has done, a number of phenomena, differing so obviously in their nature, as those that occur in the different functions of the animal economy, and in the various textures, systems, and organs subservient to these, to the agency of one common principle or power-Excitability-at a period when the distinct provinces of the Muscular and Nervous Systems, and their respective influence in the functions of Muscular Contraction, of Sensation, of Volition, and of involuntary Innervation, had been recognised, investigated, and distinctly pointed out by several physiologists and pathologists, and in particular, by Haller, Whytt, Bordeu, and Cullen. Indeed, Dr Brown's reference of all the phenomena of the different systems and organs of the animal economy, to the agency of one common principle, does not seem to be more philosophical in its object than the attempt made by some of the ancients to refer all the phenomena of the universe to the agency of one common element; or, than it would be in modern times, to ascribe all the sensible changes Q

VOL. II.

resulting on the surface of our globe from the action of the masses and molecules of different kinds of matter on one another, to the principle of Gravitation alone, to the exclusion of the co-operating principles of Heat, Light, Electricity, Magnetism, and Chemical Affinity.

IV. "A certain quantity, or a certain energy of Excitability is assigned to every individual system upon the commencement of its living state. The measure of the energy or quantity of this property is different in different animals, and in the same animal at different times and under different circumstances. The effect of the operation of the exciting powers upon the excitability, is to wear it out. The more weakly that stimuli act upon it, it becomes the more accumulated, abundant, or languid; and the more powerfully they act, it is the more exhausted or consumed. The incapacity for stimulus may go so far as that the smallest portion of stimulus will put an end to life." (Elements, § 18, 24. Outlines, § 12, 15, 16.)

It is difficult to understand what the precise idea was which Dr Brown wished to express, by affirming that a certain quantity or energy of excitability is assigned to every being on the commencement of its living state: whether he meant to affirm, as his words seem to import, that every organized being receives its whole stock, or sum total, as he himself expresses it (Elem. § 70), of excitability at the commencement of life; and that this stock, as his account of the effect of the operation of exciting powers necessarily implies, undergoes a gradual but constant diminution from the stimulant operation of all the powers that act upon living systems: --or whether he meant merely to maintain the less ques

tionable but nugatory proposition that every being, on the commencement of its living state, is endowed with a certain quantity of the living principle, or vital power, which is capable of being increased and diminished by the application and abstraction of stimuli. It is obvious, however, that it is in this last sense only that any definite meaning can be attached to the very frequent use which is made in the Brunonian system, of the terms Accumulation and Exhaustion of Excitability.

Dr Cullen, in proposing the Theory of Excitement, had rejected the terms of accumulation and exhaustion, employed previously to his time in the explanation of the doctrine of the animal spirits, as inapplicable to those conditions of the animal power or energy of the brain, upon which he conceived the states of sleeping and waking, and of vigour and debility, to depend; conditions which he regarded as consisting simply in the more or less excitable state of the nervous system (see vol. i. p. 310). But Dr Brown, in adopting from Dr Cullen the Theory of Excitement, resumed the use of the expressions of accumulation and exhaustion, and by doing so, has involved himself in some of those contradictions with which he has been charged by the opponents and critics of his doctrines.

In an able article on the writings of Dr Brown, inserted in the first volume of the Edinburgh Medical and Surgical Journal, by my late very intelligent and experienced friend Dr Kellie of Leith, it has been justly remarked, that "Dr Brown has made no provision in his system for the recovery of exhausted excitability, which, indeed, would have been perfectly inconsistent with the fundamental principle of his doctrine, viz. that a determinate portion of excitability is assigned to every in

dividual at the commencement of its existence. That this determinate portion should be acted upon by stimuli, gradually wasted by their regular operation, or suddenly exhausted by the inordinate action of the more energetic, is intelligible enough, and perfectly congruous to the theory; but that this excitability, the quantum of which is originally so exactly proportioned and so nicely determined for each individual, should, after being consumed, ever again accumulate by any interruption in the application of those stimuli, is neither clear, intelligible, nor consistent Upon the principle, indeed, thus gratuitously assumed, the excitability might be economized, but never could be increased, never made to accumulate above what remained at the time any proportion of stimulus was withdrawn; though something might be saved, nothing could be gained by the abstraction of stimuli; and on the re-application of the discontinued stimuli, or of others, the excitability should never be found increased or accumulated, but should be stationary at the point of interruption; or more correctly, in every possible case, should be found somewhat wasted, though less than it otherwise might have been, inasmuch as it must have been acted upon, and consequently consumed more or less by the other continued stimuli, in proportion to their number and power. * On the other hand, every additional, unusual, and violent stimulation should, upon the same principle, rapidly waste and hasten

* In reference to this opinion of Dr Brown's, Professor Vacca of Pisa has observed,—" We may form an idea of the logic of this author from the following reasoning: Excitability is of a determinate degree in each individual, and is continually consumed by an external power, but sometimes in larger and sometimes in less quantity. When it is consumed in a lesser degree, instead of diminishing it increases! This seems to be nearly the same as to say, I have a purse containing 200 pieces of money. In general I take out six pieces every day, but some days I take two only; and whenever I take only two, the number of the pieces of money is increased! Risum teneatis amici."

the irrecoverable exhaustion of the powers of life. The proposition, then, that a determinate portion of excitability is assigned to every individual, being equally inconsistent with the subsequent theorems of the system and with matter of fact, must be given up, or explained away somehow. This the later, or Pseudo-Brunonians, have attempted; or they have yielded the point so far as to admit that the wasted excitability may, by rest and food, be partially renewed, though it does not entirely regain the point where the exhaustion had commenced.' This concession, however awkwardly and sparingly made, is, in truth, an acknowledgment of oversight in that brilliant system which challenges all reproof, and by no means a refutation of the critique of Hufeland, who had before pointed out the inconsistency of this principle."

It would be endless to enumerate all the contradictions in which Dr Brown was involved by his theory that life consists in, or depends on, the gradual exhaustion of the stock of excitability which every being receives at the period of its formation. As examples, it may be sufficient to mention his declaration, that the more abundant the excitability is, the more it is languid (Outlines, § 12), the more easily it is saturated, and the less stimulus does it admit (ibid. § 14); that the greatest degree of excitement is produced by the action of a stimulus of a medium force on a half-wasted excitability (Elements, § 25); that the excitability may be increased by being less wasted (Elem. § 24, 32, 39); and that death, which, he says, is a consequence of a perfect extinction of the excitement, may arise either from a complete exhaustion or an ultimate abundance of the excitability.

V." As some of the Exciting Powers act by evident