This supreme governor occupies, then, pretty much the position of a gifted monarch who performs the part of his own prime minister without thereby limiting the spontaneous action of any minister in his own department, or of the president of a republic who disdains being, like a constitutional prince, merely the dot upon the i, and not only reigns, but also actually governs. Thus the organism, as model of an artistic union of guiding-head, independent provincial government, local self-government, and individual self-activity, keeps the right mean between democratic anarchy and centralised autocracy.1 What this organisation of Nature has least affinity with is the constitutional system with its parliamentary machinery and the ideal brutality of its government by majorities. However, it would perhaps be hazardous to reproach Nature that it also has not followed this doctrinaire model, which, until quite recently, passed pretty generally as the ideal of political organisation. It were rather worth considering whether, conversely, our modern political wisdom might not derive a stimulus to fresh revision of its doctrines from the study of the arrangement of the natural organism.
Through the provinces being in great part not demarcated from one another by localisation of the sphere of government, but by the qualitative difference of offices, there results the peculiar phenomenon that each province of the body is represented in more than one brain-centre, and according to the nature of the stimulus or motive can derive its impulses of innervation now from this, now from that centre. This result is one of the most important achievements of modern nerve - physiology, and thoroughly disposes of the popular prejudice that for every province of the body a single corresponding centre has to be sought in the brain. Undoubtedly the brain forms in a certain sense a reflected image of the whole body according to its provinces of innervation. It is also correct that this reflected image is in one respect simpler than the original, namely, so far as a physiological element in the centre corresponds to a sphere of motor innervation of relatively considerable extent, whose joint action is effected by the former by means of a single impulse. But in another direction the reflected image is more complete than the original, because it does not offer a single, but (like the image of a mirror cut with facettes) a repeated reflection (W., p. 227–228). In this way, e.g., all the provinces of the body are represented both in the cortex of the cerebrum and in that of the cerebellum, and, moreover, even in the optic thalami and in the corpora striata, and, lastly, by far the largest part once again in the spinal cord, including the medulla oblongata. One and the same movement of a bodily province, namely, can be innervated by a reflexion from the spinal cord or medulla oblongata, or be excited by the optic thalami on occasion of tactile sensations, or be called forth by the cerebellum to preserve one’s balance, or spring from the corpora striata, which have received their impulse from the cerebral hemispheres, or, lastly, perhaps be also produced directly by the latter (with evasion of all the other centres except the spinal cord).
Now every one of the centres which have been named (with the exception of the cerebral hemispheres) can again send the same motor impulse downwards on two sorts of occasions, or in each of these centres the stored-up energies can be set free in one of the directions pre-designated by the existing tendencies by means of stimuli of two different kinds: firstly, through such as are conducted from below, and secondly, to such as are conducted from a superior centre. The former are the perceptions conveyed by sensory nerves, the latter are the result of the direct action of the higher governing bodies; in both cases the centre in question reacts independently, conformably to its individual purpose, on the received stimulation; in both cases we have therefore to do with a reflex act, which reveals the inner teleology of the independent mode of action of the centre (W., p. 830).
Marshall Hall had based his reflex theory on the assumption of separate paths for reflexes on the one hand, and for the sensory and motor excitements leading to and coming from the brain on the other. This assumption can, however, be established neither physiologically nor anatomically; on the contrary, everything favours the identity of both paths in the sense just explained. In the more simply constructed spinal cord of fishes anatomical inquiry renders it directly probable “that the same ganglion cells which give off motor fibres to the nerve-roots effect by ascending processes a union with the more highly situated motor centres, and by others running backwards with the sensory parts” (W., p. 121–122).
It is clear that an arrangement of the sensory and motor paths making possible the mode of action laid down, must correspond to the repeated reflexion of all or very many provinces of the body by means of the different centres. We may connect with this what was remarked above in Section 3 on conduction in the spinal cord. We there saw how the possibility of the reflexes of the spinal cord was bound up with the further conduction of the stimuli of sensation to higher centres. In the uppermost part of the spinal cord or in the medulla oblongata all the motor and all the sensory fibres unite into a motor and a sensory main path, each of which again divides in the medulla oblongata into several branches. The main motor path first divides into two main branches, of which one leads through the peduncle of the cerebrum to the fore-brain, and the other to the parts of the middle-brain. The former remains purely motor, the latter enters in the centres, where it terminates, into direct connection with parts of the sensory path. The former divides into two sub-divisions, of which one directly leads to the motor part of the cortex of the cerebral hemispheres, whilst the other terminates in the corpora striata and nucleus lenticularis; the latter main branch, on the other hand, divides into three subdivisions. Of these, the one leads through the laqueus to the corpora quadrigemina, the others through the tegmentum to the optic thalami, and the third finally to the cerebellum (W., p. 165).
Thus we see how each of the different centres has its share in the main conduction which leads downwards to the provinces of the body. That, for the rest, each of these ramifications not merely represents a part of the corporeal provinces, but all taken together, is only made possible by this, that all the conducting fibres are interrupted both on their entrance into the spinal cord, and also further above by ganglion-cells, so that an association of many conducting fibres coming from below repeatedly takes place by means of the grey matter, and a carrying forward of the conduction in an upward direction through several co-ordinate fibres, each of which has now the same significance for all the conducting fibres below in connection with it.
The course of the chief sensory path is in this distinguished from that of the motor path, that only a small part of it leads directly to the cortex of the cerebrum; a second branch turns here too to the cortex of the cerebellum, and a third in several subdivisions to the anterior and middle ganglia of the brain (W., p. 165–166). The latter branch offers here, at all events, a partial compensation for the small size of the branch leading direct to the cortex of the cerebrum, because it is to be assumed that the consciousness of the hemispheres receives the chief part of its sense-perceptions (with perhaps the sole exception of the perceptions of hearing) only through the intervention of the sensory ganglia, which work up the stimuli of the sensory nerves independently into orderly and complete perceptions. The sensory paths to the great hemispheres, whether direct or through the sensory ganglia, seem to find their central ending in such districts of the cortex as lie behind the fissure of Sylvius, so that thus in general the anterior parts of the cortical layer are to be regarded more as motor, the posterior more as sensory, central parts (W., p. 167), and would stand in a similar relation to one another as the anterior and posterior columns of the grey matter of the cord.
The varied manner whereby one and the same movement may be set up, and the variety of the intermediate stages which a motor impulse issuing from the cerebral hemisphere can traverse, afford a clear insight into the relative facility with which, on the functions of a centre being disturbed, an adjustment can take place by the vicarious action of other centres. One can, of course, here not leave out of sight the fact that pathol
ogical processes for the most part acquire in course of time a wider distribution, and thereby frequently again destroy the adjustment which has already taken place. That, however, even in those cases where only a single centre loses its functions there occurs a strong disturbance of all motor phenomena, is an argument in favour of the view that in normal circumstances the path for any complex movement innervated by the hemispheres is that which is best exercised and usually employed.
Complete incapability of motion or paralysis is therefore only induced by arrest of the function of several chief centres, or by interruption of the chief motor path from the brain to the body. An incomplete paralysis, however, presents an entirely different picture, according as the disturbance of function or arrest of conduction relates to the Fore-brain or to the Intermediate, Middle, and Hind brains. In both cases the execution of all movements is still possible; but in the former case it occurs only as involuntary movement of reflexion or regulation; in the latter case only as voluntary movement. If the arrest of function concerns the Fore-brain or the crus cerebri, the influence of conscious will (innervation of the hemispheres) is impaired, but the involuntary movements remain untouched by it (paresia). On the other hand, if the arrest of function concerns the middle parts of the brain or the paths leading thereto (laqueus and tegmentum), the conscious will (after overcoming the first disturbance) retains, it is true, its sway over every single province of innervation, but the regulation and involuntary combination of movements is wanting (ataxy). In the former case, the sick person has to make great efforts to overcome the arrest of function by the innervation of the hemispheres, and his movements become truly troublesome and difficult, his gait dragging. In the latter case, the will of the hemispheres must see to all the detail of movement, for which, in other cases, the subordinate centres would make far better provision, and the movements thereby become unsure (even perhaps trembling), the gait hesitating (W., p. 205–206).
A question which must not be left undiscussed is the following:—On what does it depend whether a stimulus affecting the periphery of the body liberates at once a reflex reaction in the particular spinal centre, or only in some one of the higher centres? The mere strength of the stimulus alone cannot here be decisive; for it is indeed true that a stimulus propagates with certainty its excitation to a greater height the stronger it is, and that no centre remains closed to the strongest stimuli; but, on the other side, we also know that the weakest of all stimuli are able to reach the cerebral hemispheres, and that in the normal state of waking life reflexes of the subordinate centres can only be set up in consequence of a relatively very small part of all the stimuli affecting the organism. This state of things is explained by the general law that, as the ganglion-cell exerts on the nerve-fibre an influence, so every higher centre on those subject to it, which simultaneously lowers the reflex irritability of the lower centres, and diminishes the resistance in conducting to the higher centre. This centrifugal current of innervation, inhibitory in respect of the spontaneity of the lower centres but helpful for the perception of the higher centre, exists, in the first place, as a persisting tone in the whole nervous system; secondly, it is reflectorially called forth in a more intense degree on the preliminary announcement of stimuli; and, thirdly, it can be voluntarily sent out from the cerebral hemispheres as result of a conscious reflex process. The latter case gives us the psychological interpretation of the inner nature of this current of innervation, which now appears on its negative side as inhibiting will, on its positive side as attention.
It is well known that the involuntary inclination to reflex movements (e.g., to shrink on being tickled, or to dance with expressive dance-music) may be suppressed by the conscious will, which must have different degrees of energy according to the strength of the reflex tendency. This however means, in physiological language, that the cerebral hemispheres may innervate the reflex centres in question in such a way that their reflex irritability is momentarily lowered, or that their tendency to reflexion is paralysed by negative impulses. To the same series of phenomena belongs the fact that the conscious will in the healthy waking state keeps in check the instinctive impulses which are rooted in lower central organs (e.g., food- and sex-instinct), but that in dreams, when the activity of the cerebral hemispheres is enfeebled, or on morbid disturbance of the same, these impulses press forward in ruthless and shameless fashion, and in madmen, e.g., often enough seek their satisfaction without restraint in the crudest fashion. It is teleologically of the highest importance that the reflex actions of the lower centres only display their unchecked activity precisely when the cerebrum is deprived of power by sleep, or is claimed by another direction of the attention; it is just the same as in political life, where the governor of a province only acts without reserve on his own initiative, when the prince is not present to take his supreme resolves, or if he be otherwise occupied, and cannot therefore concern himself at the moment with the affairs of a province.
I have (comp. vol. i. p. 131–132, 174–176, 275–276, and vol. ii. p. 105–108) represented attention as a centrifugal current of innervation facilitating conduction, which may be caused partly by reflex ideation, partly by ingoing stimuli, and this often-impugned conception is confirmed in all the main points by the thoroughgoing investigations of Wundt (W., p. 717–725).
Suppose some one is reading a book, and a person present in the room puts a question to him; undoubtedly the subject of the question will not immediately affect the consciousness of his hemispheres, but yet the latter have been stimulated. It is, as it were, a notice-signal, such as the telegraphist sends before forwarding a dispatch. This stimulus suffices to turn reflectorially the current of innervation of attention in this particular direction, and the result is, that the consciousness of the hemispheres after an interval takes notice of the question perceived in the auditory centre, and not yet obliterated there. Here appears the importance of highly developed independent sensory ganglia, which perceive the impressions as ordered perceptions before the consciousness of the hemispheres notes anything of the occurrence of a perception.
In the same way as the cerebral hemispheres send forth the innervation-current of attention and of the arrest of the will to the sensory ganglia and sensori-motor centres as reflexion on the stimulus provisionally conducted thither, in the same way must we conceive such currents as radiating from the middle parts of the brain to the sensory nerves and to the medulla oblongata and spinal cord, and from every superior part of the medulla oblongata and spinal cord to every lower part of the same, partly as persisting tone, partly as momentary reflectorial strengthenings of this tone. On the persisting tone of this inhibitory current depends the balance of chemical composition and decomposition in the lower centres, i.e., their nutrition (M., p. 179), in like fashion as that of the nerve-fibre on the inhibitory current of the ganglion-cell from which it springs (comp, above, Section 2). “The increased irregular activity” (in comparison with the co-ordination effected by higher centres) “of the lower centres that have escaped from control betokens degeneration: it is like the turbulent, aimless action of a democracy without a head” (M., p. 179). This must never be forgotten in the consideration of the appropriateness of the reflexes of the lower nerve-centres, that they only fulfil their normal, proper, and most frequently proposed task on the supposition of the presence of higher guides, to whose orders they readily submit; that the reflex action on commands coming from above is the usual case, and reflexion on a peripheral stimulus in the absence of higher instructions only the rarer exception.
The influence of the inhibitory current coming from above is experimentally demonstrable, and that too in a twofold way. Namely, if a part of the nervous system be separated from its higher centres, the inhibitory current is interrupted, and this interruption comes immediately to manifestation in the considerably increased irritability of the part isolated above. If, on the other hand, the connection of the parts remains unaffected, but higher centres be stimulated (e.g., the upper part of t
he spinal cord) by stimuli conducted thither, their heightened activity makes itself also manifest in a strengthening of the inhibitory current, i.e., the irritability of the lower centres is now found to be reduced below the normal state (W., pp. 174 and 118). The enhancement of the irritability of the lower centres in the first case is also demonstrable by slicing away the hemispheres and adjoining parts from above downwards. These experiments, in conjunction with preliminary psychical observations, are quite decisive, and unambiguously prove the artistic and purposive organisation of the nervous system, in which the lower energies are kept, it is true, prepared and always ready for action, but, at the same time, are held in check by the superior authorities, as a squadron of skilful riders and snorting steeds by the will of the leader, until the moment seems to have arrived for unchaining these energies by a nod.
12. Organism and Soul. —After the foregoing expositions it can hardly be necessary to point out that, in the present state of nerve-physiology, the old question as to “the seat of the soul,” which in philosophical reference could only have been raised by an erroneous metaphysic, is now deprived of all significance on the physiological side also.
The older philosophy could only propose this question so long as it, in the first place, looked on the soul as a metaphysical individual, independently existing apart from the organism belonging to it (monad); and, secondly, as subjected to objective-spatial determinations, being, e.g., of punctual magnitude and locally fixed. Now, one may indeed look upon the soul as psychical substance per se, but as such it is not individual (not monad). One may also regard it as psychical individual; as such, however, it is not to be conceived as freed from the body, by which alone it can be individualised. Further, one may conceive it in objective-spatial relations, but only in and through the organism, in the unity through which it alone becomes individual; abstracted from body it is non-spatial in respect to the objective real space, and can merely copy in its idea a subjective-ideal space according to the former. The soul conceived in its separation from the body is thus not individual and non-spatial, and there can be no talk of a place or seat of the same; the soul understood as organic-psychical individual is just as long, thick, and broad as the body or living organism, and cannot have any seat in it.
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