Problems of Life and Mind. Second series, George Henry Lewes [e book reading free TXT] 📗

href="@public@vhost@g@gutenberg@html@files@60212@60212-h@60212-h-39.htm.html#Footnote_249" id="FNanchor_249" tag="{http://www.w3.org/1999/xhtml}a">249 Indeed we have only to consider the Laughter which follows a ludicrous idea, or the Terror which follows a suggestion of danger,—the varying and involuntary expression of Emotion,—and the curious phenomena of Imitation and Contagion,—to see how large a place cerebral reflexion occupies.

46. The existence of cerebral reflexion having been thus made manifest, Dr. Carpenter classed all reflex actions under three heads: 1°, the excito-motor, determined by the spinal cord; 2°, the sensori-motor, determined by the ganglia at the base of the brain; 3°, ideo-motor, determined by the brain. From all these Consciousness is absent. From the first, he supposes Sensation to be absent. As an artifice, such a classification may have its value, but it is physiologically and psychologically misleading. It sustains the hypothesis of an imaginary excito-motor mechanism. It restricts Sensibility to one of its many modes. It fails altogether to connect Sensation with Thought, the Logic of Feeling with the Logic of Signs.

47. The view of Sensibility as common to the whole cerebro-spinal axis is by no means new. Robert Whytt maintained it. Prochaska held that the spinal cord formed the greater part of the sensorium commune; and he adduced, in proof, the familiar facts of sensibility manifested by headless animals. The next writer whom I can discover to have held this opinion is J. J. Sue,—the father of the celebrated French romance-writer,—who, in 1803, conceived that his experiments proved the spinal cord to be capable of replacing, to a certain extent, the functions of the brain.250 Next came Legallois,251 who undertook to show, by a series of experiments, that the principle of sensation and movement, in the trunk and extremities, has its seat in the spinal cord. The mere division of the cord, he said, produces “the astonishing result of an animal, in which the head and the body enjoy separate vitality, the head living as if the body did not exist, and the body living as if the head did not exist. Guinea-pigs, after decapitation, seem very sensitive to the pain caused by the wound in the neck; they alternately carry first one hind-leg and then the other, to the spot, as if to scratch it. Kittens also do the same.”

A few years afterwards, 1817, Dr. Wilson Philip concluded that “the spinal marrow possesses sensorial power, as appears from very simple experiments”; but he held the brain to be the chief source of sensorial power.252 The following year, Lallemand supported this opinion by the very curious phenomena exhibited by infants born without brains: these infants breathed, swallowed, sucked, squalled, and gave very unequivocal signs of sensibility. The value of such observations consists in disproving the objection frequently urged against the evidence of decapitated animals, namely, that in these animals the spinal cord preserves the remains of a sensibility endowed by the brain.

Longet here places an observation recorded by Beyer. A new-born infant, whose brain, during the birth, had been completely extirpated (to save the mother’s life), was wrapped in a towel, and placed in the corner of the room, as a lifeless mass. While the surgeon was giving all his care to the mother, he heard with horror a kind of murmur proceeding from the spot where the body had been placed. In three minutes a distinct cry was heard. The towel was removed, and, to the surprise of all, this brainless infant was seen struggling with rapid movement of its arms and legs. It cried, and gave other signs of sensibility for several minutes.253

In 1828 Calmeil arrived at the same conclusion as that reached by Legallois, Wilson Philip, and Lallemand. Indeed when, in 1833, the Reflex Theory appeared, this opinion was so firmly rooted, that we find Mr. Grainger combating it as the established error of the day. He takes as much pains to show that physiologists are wrong in attributing sensation to the spinal cord, as I am here taking to show that they were right.254 “It is, indeed, apparent,” he says, “that the whole question concerning the truth or falsehood of the theory which attributes the reflex power to the spinal cord hinges upon the correctness or incorrectness of the received doctrines respecting the seat of sensation and volition; so that until those doctrines are proved to be false, it is impossible to establish the hypothesis of Dr. Hall.”255

The reader is requested to take note of this, because when we come to the evidence which proves the spinal cord to be a centre of sensation, we shall find that the only ground for rejecting that evidence is the assumed truth of the Reflex Theory, coupled with the assumption of the brain being the exclusive seat of sensation. Whereas if the evidence proves that the spinal cord is a sensational centre, then the Reflex Theory is destroyed, and cannot be urged against such evidence.

48. Thus many of the facts which prove the sensational function of the spinal cord were known, and even a vague conception of their real significance was general, until the Reflex Theory came to explain all such facts as the results of mechanical adjustment, and of a new nervous principle called “Reflexion.” For many years this theory has reigned, and met with but little opposition. Yet the true doctrine has not wanted defenders in Germany. Nasse256 denied that decapitated animals showed no spontaneity; he asserted that they exhibited clear signs of mental activity. Carus sarcastically pointed out that the word “reflex” was replacing “irritability,” as a key to unlock all puzzles; and he took up a position which is very similar to the one occupied in these pages, namely, that the spinal cord being formed of gray matter as well as of fibres, it must have sensibility and power of reacting on nervous stimulus, no less than conductibility; that, in fact, it is a centre, and must act like all other nerve-centres.257 J. W. Arnold opposed the Reflex Theory in a very remarkable little work, in which he vindicates the claim of the spinal cord as a sensory and motor centre, although denying to its actions any volitional character.258 This was in 1844. Eleven years elapsed without any further opposition, when Edward Pflüger, in 1853, published his work on the Sensorial Functions of the spinal cord.259 In this work he recurred to the old views of Prochaska and Legallois; but although he attacked Marshall Hall with merciless severity, he did not point out the fundamental error of the Reflex Theory, which theory he seems to accept. Nor did he give his views that philosophical and anatomical basis which could alone render his interpretations acceptable. Added to this, the tone of asperity in which his work was written, created some prejudice against him; and thus, while many admitted his facts, they rejected his conclusions.260

In 1858 Professor Owen read a paper of mine at the Leeds meeting of the British Association, on “The spinal cord as a centre of Sensation and Volition,” in which a rapid indication of my point of view, and an account of some experiments to illustrate it, were given—not, I believe, conclusive to any of the audience. Indeed, the subject was too vast to be discussed in such a paper; and my object was rather to excite new inquiry, than to make converts to a view which could only be embraced after a thorough reinvestigation of the dominant theories.

In 1859 appeared Schiff’s work;261 and here we find a large space allotted to the discussion of Pflüger’s doctrine. Schiff, whose immense experience as an experimentalist, and whose acuteness and caution every one will highly estimate, frankly pronounces in favor of the sensational character of spinal actions; but he denies that they are volitional, and objects strongly to the introduction of any such idea as that of “psychical activity.” He thinks it utterly untenable to suppose that impressions have reactions in the brain which they have not in the spinal cord:—if one has sensibility, the other must have it; and he thinks that, so far from the actions of the cord being distinguishable from those of the brain by the character of “reflexion,” and depending on a mechanical arrangement—all actions, cerebral or spinal, are reflex; all depend on a mechanical arrangement.262

Since that time there has been the remarkable work of Goltz, so often cited in these pages,263 and his subsequent experiments on dogs, which (although he does not decisively adopt the views of Pflüger) furnish ample evidence that sensation and volition cannot be exclusively localised in the brain.

49. Heubel’s interesting experiments264 show that a frog may be thrown into a state of profound sleep by the withdrawal of all external stimulation, and in this state will remain lying on its back for hours. Now this position is one so very uncomfortable that, when awake, the frog will not retain it a moment, if free to turn round; and when asleep, a prick on the toe, a sudden noise, or a beam of light will awaken it, causing it to turn. That is to say, the withdrawal of the normal stimuli so lowers the sensibility of the frog’s nerve-centres, that he does not feel the effects of the unusual position, but feels them directly the centres are stimulated into activity. All this is intelligible enough on the supposition of the state of sleep being dependent on a lowering of the cerebral activity. But what shall we say on learning that precisely the same phenomena are manifested by a brainless frog? Every one knows that the brainless frog is intolerant of lying on its back, and immediately turns round, if placed on it. Yet the brainless frog may be thrown into deep sleep by the same exclusion of external stimuli; from which he also will be awakened by a prick, a noise, or a beam of light; and no sooner is he awakened than he at once turns round. Were the brainless frog incapable of sensation, a prick on his toe would cause a simple reflex withdrawal of the leg; but this is not the effect; on the contrary, the stimulus excites the whole spinal cord, and whatever sensation of discomfort may be caused by the abnormal position of the limbs in an uninjured awakened frog, is excited in the brainless frog.

50. I need not swell this chapter with examples of Sensibility in animals deprived of the brain; many have already been given, and any text-book of Physiology will supply more. No one disputes the observations, only the inference that these manifestations were sentient: they are said to have been merely mechanical reflexes. If, however, we can detect in them some evidence of what all recognize as peculiarly characteristic of Mind, the mechanical interpretation will be less plausible.

At the outset the reader must be warned against exaggerating and distorting the bearing of my remarks, and must not suppose that I disregard the vast differences between the Logic of Signs which belongs to Thought, and the Logic of Feeling which belongs to Sensation, nor suppose that I look upon the spinal cord as a mental organ having the same functions as the brain. All that I wish to establish is the common character of spinal and cerebral processes, modified as each is by the character of the actions initiated by the process.

51. This premised, let us begin with the evidence of

DISCRIMINATION.

Although this process is usually regarded as purely psychological, it must obviously have its physiological side; we find it in Sensation