Problems of Life and Mind. Second series, George Henry Lewes [e book reading free TXT] 📗
- Author: George Henry Lewes
- Performer: -
Book online «Problems of Life and Mind. Second series, George Henry Lewes [e book reading free TXT] 📗». Author George Henry Lewes
41. The difference between a voluntary and involuntary act is not, I conceive, that in the one case the brain co-operates and in the other is inactive, but that while in both the brain co-operates, the state of the sensorium known as mental prevision or ideal stimulation, is present in the one, and absent or less conspicuous in the other. So likewise the difference between a normal reflex action accompanied, and the same action unaccompanied by consciousness, is not that the brain co-operates in the one and is inactive in the other, but that the state of the sensorium is somewhat different in the two cases. Movements which originally were voluntary and difficult of execution—accompanied therefore by brain co-operation—become by frequent repetition automatic, easy of execution, and unconscious—they are then said to depend on the direct action of the established mechanism. Granted. But what are the components of this mechanism? Are they not just those centres and organs which at first effected the movements? In becoming easy and automatic, the movements do not change their mechanism—the moving organs and the motor conditions remain what they were; all that is changed is the degree of consciousness, i. e. the state of the sensorium which precedes and succeeds the movement. It is this which constitutes the difficulty of the question. Some readers may consider that all is conceded when unconsciousness is admitted. But this is not so. My present argument is the physiological one that the brain co-operates in reflex actions whenever the brain is structurally united with the reflex centres; the psychological question as to whether consciousness is also involved in this brain co-operation must be debated on other grounds; and we have already seen that consciousness operates in gradations of infinite delicacy.
Observe a man performing some automatic action, such as planing a deal board, or cutting out a pattern, which he has done so often that he is now able to do it “mechanically.” It is certain that his brain co-operates, and that he could not act thus with an injured brain; yet he is said to act unconsciously, his brain occupied elsewhere as he whistles, talks to bystanders, or thinks of his wife and children. Yet the brain is acting as an overseer of his work, attentive to every stroke of the plane, every snip of the scissors; and this becomes evident directly his attention is otherwise absorbed by an interesting question addressed to him, or an interesting object meeting his eye: then the work pauses, his hands are arrested, and the automatic action will only be resumed when his attention is released—when he has answered your question, or satisfied himself about the object.
42. This is a step towards understanding the co-operation of the brain even in those connate reflexes which were not originally voluntary acts, but were from the first organized tendencies, and are capable of being realized in the absence of the brain. I admit that it is difficult to find proof of brain co-operation here, though I think the anatomical and physiological evidence render it highly probable. But distinct proof to the contrary would not suffice for the Reflex Theory—would not prove that reflex actions were insentient—unless there had previously been proved that which seems to me contradicted by the clearest and most massive evidence, namely, that the brain is the sole seat of sentience. This contradictory evidence we will now furnish.
INDUCTIONS FROM PARTICULAR OBSERVATIONS.
43. In the last chapter we surveyed the deductive evidence, from which the conclusion was that Reflexion necessarily involves Sensibility, but not necessarily any one particular mode of Sensibility, such as Consciousness, Pain, Discomfort, Attention, or the reaction of any one of the special Senses. Although each or all of these modes may be involved in the sensorial process which determines a reflex act, each or all may be absent. Such is the fact of observation. This fact is interpreted on the hypothesis that Reflexion is the exclusive property of the spinal cord, as Sensation is of the brain. When we come to examine the evidence for this hypothesis, we find it to move in a circle: the brain is said to be the exclusive seat of sensation, because reflex actions can be effected after its removal; and reflex actions are said to be insentient because they take place in the absence of the brain.
A gentleman was one day stoutly asserting that there were no gold-fields except in Mexico and Peru. A nugget, dug up in California, was presented to him, as evidence against his positive assertion. He was not in the least disconcerted. “This metal, sir, is, I own, extremely like gold; and you tell me that it passes as such in the market, having been declared by the assayers to be undistinguishable from the precious metal. All this I will not dispute. Nevertheless, the metal is not gold, but auruminium; it cannot be gold, because gold comes only from Mexico and Peru.” In vain was he informed that the geological formation was similar in California and Peru, and the metals similar; he had fixed in his mind the conclusion that gold existed only in Mexico and Peru: this was a law of nature; he had no reasons to give why it should be so; but such had been the admitted fact for many years, and from it he would not swerve. He was not fond of new-fangled notions, which, after all, would only lead us back to the exploded errors of the past. To accept the statement that gold was to be found elsewhere than in Mexico and Peru, would be to return to the opinion of the ancients, who thought there was gold in the upper regions of Tartary!
Sensation is not tangible, assayable, like gold. We can understand, therefore, that the very men who would make merry with the auruminium, would accept easily such a phrase as “reflex action.” The decapitated animal defends itself against injury, gets out of the way of annoyances, cleans itself, performs many of its ordinary actions, but is said to do these things without that Sensibility which, if its head were on, would guide them. Even before the Reflex Theory was invented this line of argument was used. Gall, referring to the experiments of Sue, previously noticed, says that “Sue confounds the effects of Irritability with those of Sensibility.”246 Not gold, dear sir, but auruminium!
44. On investigating the phenomena we soon come upon two classes which must cause hesitation. We find that the brain has its reflex processes, of the same order as those of the cord; we find that these processes may be conscious or unconscious, voluntary or involuntary; so that we can no longer separate brain from cord on the ground of Reflexion. In this respect, at least, the two are mechanisms with similar powers. Turning now to the other class of phenomena, we find that precisely as the brain is an organ of Reflexion, the cord is an organ of Sensation. All the evidence we can have, from which to infer the presence of sensation, is furnished by the sensorial processes in the cord. Remove the brain, and the animal still manifests Sensibility, and this in degrees of energy and complexity proportional to the mechanisms still intact: some of these manifestations have the character of volitional actions, some of automatic actions, some of Memory, Judgment, and selective Adaptation. These we observe not indeed with the energy and variety of such manifestations when the brain co-operates, since the disturbance of the organism which is the consequence of the brain’s removal—or the meagreness of the organism which is the correlative of the brain never having been developed—must of course involve a corresponding difference in the observed phenomena; but the point here brought forward is that phenomena of the same order are manifested by organisms with or without a brain.
45. Let us go seriatim through the evidence of these two classes:—
CEREBRAL REFLEXES.While Theory separated the actions of the cord from those of the brain on the ground of their being at times unconscious and involuntary, Observation disclosed that this distinction could not be maintained.
This step was taken by Dr. Laycock in 1840. In a striking paper247 read by him at the British Association in 1844, he brought together the evidence on which his view was founded. The idea has been adopted and illustrated in the writings of Dr. Carpenter, who now calls the action “unconscious cerebration.”
“I was led to this opinion,” Dr. Laycock says in announcing his view, “by the general principle that the ganglia within the cranium, being a continuation of the spinal cord, must necessarily be regulated as to their reaction on external agencies by laws identical with those governing the spinal ganglia and their analogues in the lower animals. If, therefore, the spinal cord is a centre of reflexion, the brain must also be one.” It is a matter of regret that Dr. Laycock did not extend this principle, and declare that whatever was true of the properties of the cranial centres must also be true of the spinal centres; if the brain have Sensibility, the spinal cord must also have it.
Dr. Laycock refers to the curious phenomena of Hydrophobia in proof that reflex actions may be excited by the optic nerves, or by a mere idea of water. When a mirror was presented to a patient, the reflexion of the light acting on his retina, in the manner of a reflexion from the surface of water, produced a convulsive sobbing, as in the attempt to swallow water, and the patient turned aside his head with expressions of terror. Money was given him to induce him to look a second time, but before he had looked a minute the same effect was produced.
The idea of water excited similar convulsions. No sooner was it suggested that the patient should swallow a little water than he seemed frightened, and began to cry out. By kindly encouragements he was brought to express his willingness to drink, but the sound of the water, as it was poured out again, brought on convulsions. In another case, “on our proposing to him to drink, he started up, and recovered his breath by a deep convulsive inspiration. On being urged to try, he took a cup of water in one hand and a spoon in the other. With as expression of terror, yet with great resolution, he filled the spoon and proceeded to carry it to his lips; but before it reached his mouth his courage forsook him, and he was forced to desist. He repeatedly renewed the attempt, but with no more success. His arm became rigid and immovable whenever he tried to raise it to his mouth, and he struggled in vain against this spasmodic resistance.”
In 1843 Griesinger—who appears to have known nothing of Dr. Laycock’s paper—published his remarkably suggestive memoir on Psychical Reflexes,248 in which he extends the principle of Reflexion to all the cerebro-spinal centres. The whole course of subsequent research has confirmed this view; so that we may say with Landry, “L’existence du pouvoir réflexe dans l’encéphale ou dans quelques unes de ses parties établit une nouvelle analogie entre le centre nerveux cranien et la moelle épinière.”
Comments (0)