Front Page Titles (by Subject) CHAPTER IV.: REFLEX ACTION. - The Principles of Psychology
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CHAPTER IV.: REFLEX ACTION. - Herbert Spencer, The Principles of Psychology 
The Principles of Psychology (London: Longman, Brown, Green and Longmans, 1855).
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§ 182. Under its simplest and most general form, Reflex Action is the sequence of a single contraction upon a single irritation. A vague manifestation of this sequence marks the dawn of sensitive life. Omitting those which he on the border line of the two kingdoms, animal organisms are broadly distinguished from vegetable organisms by the peculiarity that they move on being touched, or otherwise impressed. Even the almost structureless ones, respond in a more or less decided way to external excitements; and it is mostly in consequence of their response that they are concluded to be alive. But though, in the movements of these lowest creatures, reflex action is foreshadowed, it is only when we ascend to those in which there exists something like a nervo-muscular apparatus, that reflex-action proper is exhibited. In these, the response is effected not through the agency of the one uniform tissue constituting the creature's body, which is at once irritable and contractile; but the irritability is confined to one specialized tissue (nerve), and the contractility to another specialized tissue (muscle); and the two are placed in such relation that the irritation of the one is followed by the contraction of the other. Some impression is made upon the peripheral termination of a nerve; this impression is propagated along the nerve until it reaches a ganglion; there some action is set up which is propagated along another nerve proceeding from the ganglion to a muscle; and thus the stimulus carried through an afferent nerve to some inner centre of communication, is reflected from it through an efferent nerve to the contractile agent. In this simplest form of psychical action, we see a single internal relation adjusted to a single external one. Any one of the many suckers on the arm of a cuttle fish that has been separated from the body, will, under the influence of its own independent ganglion, attach itself to a substance placed in contact with it—the established or organized relation between the tactual and muscular changes in the sucker, is parallel to the uniform relation between resistance and extension in its environment—the inner cohesion of psychical states, is as absolutely persistent as is the outer relation between the attributes. And if we remember that in the daily actions of the creature, this inner relation is perpetually being repeated in response to outer one; we see how the organization of it in the species, answers to the infinitude of such experiences received by the species.
§ 183. Reflex action being the lowest form of psychical life, is, by implication, that which is most nearly related to the physical life—that in which we see the incipient differentiation of the psychical from the physical life. This truth may be discerned from several different points of view.
It was pointed out that, in all probability, the contraction seen in the lowest animal organisms when they are touched, or otherwise stimulated, is the result of an increased vital action which the stimulus produces in the adjacent tissues; and though one of these reflex contractions, as of a cephalopod's sucker, is effected in a different and much more complicated manner, yet the action, generally considered, does not so far differ as to seem properly transferable to a higher category. Mostly, it would be considered as a misuse of words to call it in any sense psychical. And though as belonging to the order of vital changes which, in their higher complications, we dignify as psychical, it may be held necessary to classify it as psychical; yet it must be admitted that in position it is unquestionably transitional.
Again, it is to be remarked that in highly organized creatures, the physical life is itself regulated by reflex action. Those rhythmical movements of the alimentary canal which follow the introduction of food, are of reflex origin; as no doubt, also, are those secreting processes by which, under the same stimulus, the digestive fluids are prepared and poured out. Moreover, the various viscera, performing each its separate function, must have their relative activities adjusted—the several processes in the maintenance of which the physical life consists, must be harmonized; and it is held that the due balancing of them is effected by reflex action. The presumption is, that the changes in the state of each viscus are impressed upon the nerves proceeding to ganglia in the Sympathetic, whence they are reflected to the other viscera; and thus their respective activities are co-ordinated.
In yet another respect may we see a close alliance between the physical life and this nascent psychical life. As was shown in a foregoing chapter, the psychical life is broadly distinguished from the physical life by the peculiarity, that its changes instead of being simultaneous and successive, are successive only; but as was also shown, this peculiarity makes its appearance gradually, and only becomes marked when the psychical life becomes high. Now the reflex actions in which the nascent psychical life is seen, are nearly as much characterized by simultaneity as are the purely physical actions. A great number of these simplest psychical changes, may be going on quite independently in the same organism at the same moment. Each of the many legs of a centipede, under the influence of its own ganglion, goes on receiving impressions and performing motions quite independent of the rest: continuing to do so after the creature has been cut in two. And on watching the wave of movements which progresses from end to end of the series of legs—seen still more clearly in a julus—it will be observed that at any moment each leg is in a different phase of its rhythmical movement; and that thus there are, at the same time, in the same organism, a great number of like changes, each at a separate stage of evolution.
Once more, the proximity of these reflex actions to the physical life, is seen in their unconsciousness. In ourselves, there are constantly going on reflex actions of which we have no immediate knowledge: as those by which the focus of each eye is adjusted to distances, and the closure of the iris to the quantity of light. Other reflex actions of which we can take direct cognizance—as that of breathing—can go on without our thinking of them. And others which are commonly accompanied by sensation—as when the foot is withdrawn from something which tickles it—are found to be most energetically performed, when, from some spinal lesion, sensation has been entirely abolished. Clearly, therefore, in those organisms in which reflex movements alone are seen, they are totally unconscious. The rapid alternations of a millipede's leg or a fly's wing, are as purely automatic as are those of a steam-engine piston; and are doubtless co-ordinated after a generally analogous manner. Just as, in a steam engine, the arrival of the piston at a certain point, itself brings about the opening of a valve serving to admit the steam which will drive the piston in the reverse direction; so, in one of these rhythmically-moving organs, the performance of each motion ends in bringing the organ to a position in which the stimulus to an opposite motion acts upon it.
But though, from all points of view, reflex action is seen to be a species of vital change very little removed from the purely physical changes constituting vegetative life; yet, it may be well to remark, that even in it, we may discern a fulfilment of the primordial conditions to consciousness. At the close of the Special Analysis (§ 100) it was shown, that in the lowest conceivable type of consciousness—that produced by the alternation of two states—there are involved the relations constituting the forms of all thought. And such an alternation of two states as is there supposed, is just that which occurs in the ganglion connected with one of these rhythmically-moving organs.
§ 184. From that lowest kind of reflex action, in which a single impression produces a single contraction, the ascent is by gradual steps to complications in the stimuli and the acts resulting from them. There is no exact line of demarcation between a single contraction and a combination of contractions. Between the excitation of dispersed muscular fibres, and the excitation of fibres aggregated into definite bundles, the transition is clearly insensible. And hence, under the head of reflex action there are classed numerous cases in which a whole group of muscular actions result from one impression. The decapitated frog which leaps when one of its feet is irritated, supplies an extreme illustration. It would, however, be alike needless and out of place to examine the varieties and complications of reflex action; to do which is the task of the physiologist rather than of the psychologist. Here it simply concerns us to note the bearing of the phenomena of reflex action upon the general argument.
We have to observe, in the first place, that these simplest of psychical changes are those corresponding to the external relations which are only one degree more specialized than the relations to which the physical changes correspond. While the processes of the purely vegetative life are in adjustment with those most general relations between nutriment, oxygen, temperature, moisture, light, which pervade the environment at large; these lowest processes of the animal life are in adjustment with the most general relations of the solid bodies contained in the environment: as those between tangibility and solidity, motion and life.
At the same time that there is so near a relation in scope between the physical life and this lowest psychical life, we have to remark, as above, that the two are closely allied in nature; not only as being both unconscious, but as both consisting of changes that are at once simultaneous and successive.
Further, it is to be noticed, that in conformity with the general law of intelligence, we see, in one of these reflex actions, an established connection between two psychical states, answering to an established connection between two external phenomena. Not that the inner tendency is exactly proportioned to the outer persistency. In many cases it is absolute in the organism, though by no means absolute in the environment. And this is just what is to be looked for in these manifestations of nascent intelligence: seeing that the adjustment of the inner tendencies to the outer persistencies, is the law of intelligence in the abstract, and cannot be fulfilled where the intelligence is incipient.
Lastly we have to note the fact, that these indissolubly connected psychical states are found to exist where there are perpetually-repeated experiences of the external relations to which they answer.