Nervous Symptoms. Generalization of normal nervous phenomena, and of their respective relations to anatomical divisions of the nervous system. Physical morbid phenomena (1) Anæsthesia, (2) Subjective sensations, (3) Paralysis, (4) Involuntary movements. Mental morbid phenomena. Causes of abnormal excitement or depression in central organs; humoral, sympathetic. Sympathies: (1) co-ordinate; homogeneous or augmentative; heterogeneous or reflex; (2) ascensive and descensive. Therapeutical control over nervous centres; cold; belladonna; strychnine; tobacco; chloroform; opium.

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GENTLEMEN: In to-day's lecture, I wish to consider with you so much of the pathology of the nervous system as relates to the analysis and interpretation of symptoms arising in that system. order to investigate such symptoms with success, you must be well informed in those great physiological results which have been increasing yearly, by the labours of all the chief anatomists of Europe, since the publication of Bell's discovery. For a complete summary, and a very just appreciation of those labours, I cannot do better than refer you to the articles published in the Cyclopædia of Anatomy, by Dr. Todd, who has himself likewise contributed largely to the elucidation of this difficult subject, and especially to the various chemical applications of nervous physiology.

In a few paragraphs I may give you those generalizations, on which hitherto we chiefly rely for our analysis of nervous symptoms. We recognize the nervous system as the sole seat of all organic changes immediately relative to the consciousness of the individual -relative (that is) to his several acts or attitudes of sensation or effort, of appetite, sentiment or passion, of judgment, imagination or will. We recognize it likewise, as the sole seat of all those intermediatory influences (independent of consciousness) which, in the living body, regulate the actions of contractile tissue, according to impressions primarily made on other tissues; as, for instance, when the iris (without our knowledge or wish) modifies its pupillary opening in consequence of a certain impression made on the skin, the cornea, or the retina.

Anatomically, we discriminate the constituents of the nervous system, as gray nerve-matter, and white nerve-matter; the latter essentially consisting of tubular elements; the former of vesicular elements; the latter essentially constituting nerve-cords, the former essentially distinguishing the nerve-centres or ganglia.

Physiologically, we recognize that aggregations of gray nervematter are the true and specific centres of nervous function; that to them converge the results of exterior impression; that from them emanate the immediate influences which determine motion; that they are terminal in respect of impression; dynamical and originative in respect of motion. We recognize that the nerve-cords are mere

channels of communication; intermediatory either between the nerve-centre and some impressible surface which affects it; or between the nerve-centre and some contractile tissue which it affects; or commissural between it and co-ordinate nerve-centres; or between it and super-ordinate and sub-ordinate nerve-centres.

For in every developed nervous system we observe a gradation in the centres of function, according to the extent of their influence. First, there is the supreme dynamical centre, which is susceptible of changes immediately and necessarily associated with the consciousness of the individual, and which more or less directly influences all other centres; this probably comprehends only the convolutionary surface of the cerebrum. Next, in at least two gradations, come the subordinate cerebro-spinal centres, which are only mediately associated with consciousness: (1) a lower grade of centres, including the special centres of individual parts, whether the material of those centres be discrete (as on sensitive nerves and in the sympathetic system) or be massed into continuous columns (as in the interior of the spinal cord); (2) a higher grade (including the gray matter of the cerebellum, of the optic thalami, and of the corpora striata) which are the centres apparently of aggregative action, standing in a first degree of subordination to the centre of consciousness, and serving intermediately to collect the impressions and regulate the phenomena of those several special centres which are subordinate to them.

The lowest nerve-centre has for its simple function to receive the notice of impressions, and to react on that notice. As the stage and mechanism of its operation, the following anatomical arrangements are necessary: a surface which may receive exterior impressions; an organ which may contract on stimulation; an afferent nerve which may convey to the centre the exterior impression; an efferent nerve which may convey from the centre to the contractile organ, that specific stimulus on which it is the latter's function to contract.

To this apparatus the whole phenomena of the nerve-centre may restrict themselves: the exterior impression, conveyed to the centre and stimulating it, may excite reaction, which reflects itself to the contractile tissue, evincing itself there in the result of motion; and thus the effect may terminate.

In the human subject (to which for obvious reasons I confine myself) it is only among parts supplied exclusively or chiefly by the sympathetic system that the subordinate centres habitually and normally act in independence of higher centres: the contractions of the heart and arteries, of the stomach and intestines, of the bronchial and Fallopian tubes, neither require that a sensation should precede, or an effort of will determine them; nor are they determinable by any voluntary effort. We shall presently see that this capacity for independent acts, which normally belongs as a habit only to the nerve-centres of vegetative life, exists as a latent function in the subordinate cerebro-spinal centres likewise, and is apt to show itself in them (in the form of characteristic reflex phenomena) chiefly when the influence of the higher centres is withdrawn.

GENERALIZATIONS OF NORMAL NERVOUS PHENOMENA. 145

In health, however, while the several segments of the nervous system fulfil their appointed functions, an impression made on any surface innervated by the cerebro-spinal axis commonly excites no reaction from those subordinate centres which lie between the impressed surface and the centre of consciousness; it is only on the latter the supreme centre-that its effect is produced; and there it is recognized as a sensation. Similarly, the movements which arise in any contractile textures under cerebro-spinal influence, do not commonly depend on the unconscious reaction of subordinate centres, primarily exerted; but depend on the energy of the highest centre, transmitted to the muscles through those subordinate centres, in the form of a volition.

The only partial exception to that rule lies in regard of certain instinctive movements, which (in all the voluntary muscles, but especially in those of respiration) are apt to occur for preservative and defensive purposes, without the previous occurrence of a distinct volition. I call it a partial exception, because such movements, though they often or usually occur in an involuntary or semivoluntary form, are yet within the distinct cognizance of the individual, are matters of sensation to him, and are controllable by his will. Of such movements you have familiar examples in the instantaneous retraction of a hand or foot that has unexpectedly encountered a sharpness-in the sudden closure of the eyelids as anything darts before them-in the convulsive cough which follows irritation of the glottis—and, indeed, in the ordinary actions of inspiration; since we can, at any moment, in our own persons, substitute deliberate voluntary breathing for that semi-conscious, semivoluntary process by which we habitually respire. It seems certain that the dynamical source of these instinctive actions lies in those accumulations of gray nerve-matter, which extend on either side, from just above the decussation of the pyramids to the floor of the lateral ventricle; which have the ganglionic centres of the higher senses and of respiration ranged around and blended with them; and which themselves (as I have said) may be considered as aggregative centres of sensible impression and motional reaction--habitually subject to the higher control of the centre of consciousness, but capable under certain circumstances of determining and maintaining definite automatic movements without the intervention and authority of that higher centre. These cerebral sub-centres of instinctive and emotional action apparently include the corpora striata, optic thalami, and those continuations of their gray nerve-matter, which extend into the medulla oblongata, under the name of fasciculus innominatus, (faisceau innominé of Cruveilhier. Acting in the abeyance of the higher centre, they are capable of exciting the several subordinate centres of the cerebro-spinal system to determinate actions; acting in union with (or rather in subordination to) the high centre, they are intermediate to the production of conscious phenomena-namely, to the inward transit of a sensation, to the outward transit of a will.

Co-ordinate with these centres in the double relations just indicated-sub-ordinate (that is to say) to the centre of consciousness,

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and super-ordinate to the spinal centres, is the third cerebral subcentre, the cerebellum; having apparently for its function to balance and harmonize those various muscular exertions of the entire body, by which, in station, progression, and athletic efforts, we unconsciously turn to the best account the mechanical endowments of our frame; a function, which is intimately associated with our impressions of direction in space-with our sense of downward, upward, forward, backward, sideward—and which seems, in its ordinary performance, to occur as an ever-fluctuating muscular equilibrium, graduated and proportioned in its several component forces, by distributive modifications of muscular tone, which are themselves reflex to impressions conveyed to the sensorium, perhaps through various channels, but specially and distinctively through the semicircular canals of the ear.*

In order to save repetition, and remove ambiguity from my analysis of an intricate subject, let me tell you here the sense in which I shall employ certain words in the course of this lecture, and in which I would advise you to employ them. By "primary centre," or "centre of consciousness," or any equivalent phrase, I mean the gray nerve-matter of the convolutions of the cerebrum, By "secondary centres," or "centres of aggregation," I mean the cerebellum, the optic thalami, the corpora striata: the second and third of these I may occasionally call "cerebral sub-centres ;" and as it is in the highest degree probable, though perhaps not yet quite susceptible of logical demonstration, that the optic thalamus is the aggregative centre of sensation, and the corpus striatum of voluntary motion, so I shall speak of them as the centres of these functions respectively, without, in each case, qualifying the phrase with some adverb of uncertainty. Remember, however, that though there is no doubt as to their joint functions as aggregative centres of sense and motion, their separate share in respect of these functions is not yet irrefragably demonstrated. In speaking of these sub-centres, too, I include under their name the gray nerve-matter which prolongs them backwards as far as the medulla oblongata. By "tertiary centres" I should imply the special cerebro-spinal centres of indi

* It was Professor Wheatstone's ingenious conjecture, that the semicircular canalsstanding always in planes rectangular to each other, and corresponding, therefore, to the three axes of solidity, would be accurate acoustic measures of the direction of sound. That they bear a definite relation to the function of the cerebellum seems a conclusion inseparable from the experiments of M. Flourens, who found that lesions of the semicircular canals produced the same in co-ordinate movements as arise from injury of the cerebellum, and that the convulsive efforts of motion which thus arise with lesion of the semicircular canals, vary according to the canal injured, just as with lesion of the different crura cerebelli: that uncontrollable forward-motion will have attended the injury of one canal or one crus; uncontrollable motion backward will have attended the injury of a different canal or a different crus; uncontrollable motion of rotation will have attended the injury of a third canal or a third crus. From these very important experiments, it would be difficult to deduce any other inference than that conveyed in the text, that the semicircular canals furnish recipient surfaces for impressions of direction in space, and that these impressions excite the cerebellum to the production of reflex phenomena, which are normally confined to the maintenance of bodily equilibrium and the co ordination of voluntary movement, by means of commensurate gradations of muscular

tone.

TO ANATOMICAL DIVISIONS OF THE NERVOUS SYSTEM. 147

vidual parts: namely (1) the gray nerve-matter of the spinal cord (which consists of innumerable special centres massed together in vertical columns); (2) the ganglia of sensitive nerves, which are discrete; and (3) those centres of special senses and special movements, which exist about the mesencephalon, and which (for convenience of package, and perhaps for readier intercourse) are grouped closely about the aggregative centres, and blended with their surface; so that while there is every physiological evidence of their distinctness, we are not able to effect an anatomical separation between them; such, for instance, is the relation of the visual centres (corpora geniculata and quadrigemina) to the thalamus, misnamed opticus. By "quaternary centres" I mean those of the so-called sympathetic system of nerves; and as I shall often have occasion to use the words sympathy and sympathetic in relation to the sense of "concurrent function," it will save obscurity if I avoid applying the same words to the nerve-apparatus of organic life, and I shall therefore speak of that apparatus throughout as the "ganglionic" nervous system. By "sensation" and "will" I uniformly imply consciousness of some objective change, or of some subjective effort: by "impression" and "motional reaction," I imply the analogous incidence of objective change, or effluence of motional stimulus, without any affection of the consciousness. By "receptivity" I mean that function of a nervous centre by which it receives and is susceptible of impressions. By "reactivity" I mean that function of a nervous centre by which it tends to excite the phenomena of muscular contraction. By "peripheral surface," in relation to sensitive nerves, I mean that tegumentary or other surface on which exterior impressions first impinge-a surface occupied by the elementary distribution of the nerve.

It will be obvious to you from what I have already said, that, in the simplest apparatus of innervation associated with the organs of consciousness, there lies, the possibility of disease under either of the following forms: viz., (1) a distal impression may fail to produce its proportionate central sensation; (2) a central sensation may exist without a proportionate distal impression having been made; (3) a central volition (or the stimulation equivalent to it) may fail to excite its proportionate muscular contraction; (4) muscular contraction may exist in parts normally under the influence of the will, without the previous occurrence of a volition, or of any equivalent stimulus. (1.) Anesthesia is the name given to the first form of diseasethat in which the patient remains without cognizance of impressions made on a surface normally sentient. It is not only in respect of the cutaneous surface and the function of touch, that this may occur. The same condition may affect other organs of sense: the visual apparatus, giving amaurosis as its result; the auditory, causing deafness; the olfactory and gustatory, producing interruption of their functions. Such disease may depend on a variety of causes. The peripheral surface originally impressed may be incapable of its function, by reason of some disorganizing process which has invaded its nervous expansion, or by reason of inflammatory products which