Metaphysical Meeting Place

Grovenor Hotel
Barsborough Room
Stained-glass Victory
CB Collection

Has a Frog a Soul,

and of What Nature Is That Soul,
Supposing It to Exist?
T. H. Huxley
Metaphysical Society (8 November, 1870)

[1] If the leg of a living frog be cut off, the skin of the foot may be pinched, cut, or touched with red-hot wire, or with a strong acid, and it will remain motionless. But, if the other leg, which remains in connection with the body, be treated in the same way, it will be instantly retracted as far as possible from the irritating agent, while the animal will show signs of pain, and attempt to get away.

If, now, the great sciatic nerve which traverses the thigh of the attached leg be cut across, irritation of the skin of the foot will produce no effect. The sciatic nerve may be traced up to the spinal cord. Just before it reaches the end of the trunk, of which it forms a part, it divides into two portions, or roots, as they are termed. One root enters the back of the cord, the other the front, and, in the cord, both roots are connected with the grey central matter of the cord. These roots may be cut separately. If the hinder root is cut, the irritation of the skin of the foot produces no effect. If the front root is cut, the hinder being left entire, irritation of the foot gives rise to signs of great pain, but the limb does not move. If that part of the spinal cord into which both roots enter is destroyed; or if only the grey matter into which they enter be destroyed, the nerve and its roots may be entire; but irritation of the skin of the foot gives rise neither to movement, nor to any sign of pain in the rest of the body. Finally, if the cord be merely cut across, above the point at which the nerve roots enter, so that these roots remain in connection with the uninjured grey matter, irritation of the skin of the foot will produce instant retraction of the legs, just as if the animal were uninjured. But it will show no other signs that can be considered indicative of pain. The body in front of the cut will remain unaffected, however great the injury done to the foot. And, at the same time, the creature will be unable to use its legs. No amount [2] of irritation of the body in front of the cut will cause it to spring, the legs being completely paralyzed for all voluntary impulses.

If the legs, with their nerves and the appertaining segment of the spinal cord, are completely removed from the rest of the body, the legs are still drawn out of the way when the skin is irritated.

These experiments prove that when the skin of the foot is irritated, a certain influence is communicated by the posterior roots of the nerve to the segment of the spinal cord; and that the segment of the spinal cord is capable of transmuting this influence into another influence, which is transmitted by the anterior roots to the muscles of the frog’s leg, and causes them to contract. The impulse transmitted to the cord is, as it were, reflected back from the cord, whence the metaphorical name of the reflex action has been given to the operation.

But it is very important to remark that the analogy of mere reflection is incomplete.

The impression on the foot may be of the simplest possible character—such as the prick of a needle—but that which is reflected down the motor nerves is a complex set of impulses, all duly adjusted, in such a manner as to withdraw the foot out of the way of the irritating body. The segment of the spinal cord, therefore, does not so much reflect the impulse it receives, as give change for it. It is not like a bell, which simply resounds when it is struck, but it resembles a repeater, which, on a simple mechanical impulse, goes through the complicated operation of striking the hour. And as in the case of the repeater, the motions to which the cord gives rise are combined towards a definite end.

As all these operations are effected just as well by the segment of the cord as by the uninjured nervous system, it is clear that they are effected independently of any sensation or volition in the rest of the body. And this is confirmed by the analogy of what occurs in man. For if the middle of the spinal cord of a man be profoundly injured, his lower limbs will pass into exactly the same condition of those of the injured frog. If the skin of the foot be irritated, the leg will be drawn up with violence. Nevertheless, the man will feel nothing, nor will he be able to draw up the leg by any effort of his own will, still less to control its action when the skin of the foot is irritated. In other words, the segment of his spinal cord is void of any connection with his consciousness and his volition. And, in [3] the absence of evidence to the contrary, it may be safe to conclude that the segment of the frog’s spinal cord is in the same position, in respect of any consciousness, or volition, which the frog may possess.

Suppose, now, that the head of another frog be cut off so as to leave the whole spinal cord in the body, in natural connection with its nerves, but to detach the whole brain, including that part in which the cord and the brain unite–the medulla oblongata .

If the frog be laid on its back, it will remain passively in that position. If one of the feet be touched with acid, the leg will be retracted, and then the two legs will be rubbed together to get rid of the irritating matter. Not only so, but if the irritated limb is placed in an unusual position, for example, drawn up at a right angle to the body, the other leg will be gradually raised up into a corresponding position, until it is so placed that it can rub away the irritating matter.

Here is evidence that the spinal cord is not only capable of giving rise to very complex combined movements, in answer to a perfectly simple irritation; but that it has a power of adjustment which enables it to meet an entirely new case—to solve a problem which could not have been presented to it under the ordinary conditions of the life of the frog.

Suppose, further, that the head has been cut off, in such a manner, that the section passes in front of the medulla oblongata, leaving this in connection with the cord, but separating it from the rest of the brain. Then the frog’s body will not lie on its back, but if so placed will exert all those complicated and condapted movements which are needed to enable it to turn over.

In all these experiments the separated head will show signs of retaining all its nervous energies. And human pathology tells us that a man’s consciousness and volition may be completely retained until the damage to the spinal cord passes so high up as to injure the medulla oblongata, when they are lost, secondarily, through the effects of such injury on the medulla. We are therefore justified, in the absence of evidence to the contrary, in concluding that anything in the shape of consciousness and volition which the frog may possess remains intact in the separated brain, under the conditions of each of these experiments.

Suppose, however, the cutting away of the nervous centres begins at the other end. Let the two hemispheres of the cerebrum be cut [4] away. The condition of the frog becomes very singular. It preserves almost all the faculties of an uninjured frog. It can see, swallow, jump, and swim; but it exerts none of these powers spontaneously. It will not even feed, but has to be fed with meat put into its throat. It is like an animal in a trance, or asleep. Nevertheless it can adjust all its movements so as to balance its body under the most difficult circumstances.1 In short, it adapts means to ends with wonderful accuracy and precision. But if more of the brain is removed, and the structures known as the optic lobes are cut away, this power is lost; and if the cerebellum is removed, the frog cannot even combine its actions so as to jump.

Facts of the general character of those detailed have long been known, and they have led to two opposite modes of conceiving of the nature of the animal frame.

By the one set of thinkers all the rationally condapted movements of the body have been referred to the operation of a soul, which they conceive to work the machinery of the body as a musician may play upon an organ or other instrument.

By the other set, it has been argued that no line can be drawn between those bodily operations of animals which are purely and obviously mechanical, and those which are purposive and apparently rational, and, therefore, that the latter may be merely the result of a mechanism too refined for us to understand at present.

It is to Descartes that we owe the most complete statement that has ever been given of the latter view. And those who have read the controversial works to which his philosophy gave rise, are aware that no doctrine of his was more frequently assailed than that of the automatism of brutes.

Ever since Descartes’ time, Physiologists have been divided into two camps, the one taking the automatic, and the other the animist side.

The father of the animists among modern physiologists was Whytt, who, in opposition to the views of Haller, maintained that a soul exists in all parts of the living body.

"I think," says Whytt, "it is not only probable, but demonstrated, that the soul does not immediately leave the body upon a total [5] stoppage of the motion of the heart, and consequently, of the circulation of the blood, i.e., upon what we usually call Death, but continues for some time present with it and ready to actuate it... Upon the whole, then, it appears certain that after death, or an entire stop of all motion in the bodies of animals, the soul still remains present with them, and can be again brought to exert its influence by various kinds of stimuli applied to their different parts. May not the same principle continue present with the several muscles after they are separated from the body, and be the cause of their motions when irritated?"2 And Whytt then goes on to refer to some very obvious objections as follows:–

"As the schoolmen supposed the Deity to exist in every ubi, but not in any place, so they imagined the soul of man not to occupy space, but to exist in an indivisible point. Yet whoever considers the structure and appearances of the animal frame, will soon be convinced that the soul is not confined to an indivisible point, but may be present at one and the same time, if not in all parts of the body, when the nerves are formed, yet, at least at their origin, i.e., it must be at least diffused along a great part of the brain and spinal marrow. Nay, while in man the brain is the principal seat of the soul, where it most eminently displays its powers, it seems to exist or act so equally through the whole bodies of insects, that its power or influence scarce appears more discernible in one part than another; and hence it is that, in such creatures, the several parts of the body live longer after being separated from each other than they do in man and other animals more nearly resembling him, where the soul seems chiefly to act in the different parts by means of their connection to the brain and spinal marrow; or at least when the cutting off such connection soon renders the parts unfit to be any more acted upon by it.

It is not, therefore, altogether without reason, that some of the greatest philosophers of the last and present age supposed the soul to be extended.3

But if the soul, without extension, be present at one and the same time at different places in the brain, and if in many animals it can [6] act along the spinal marrow for a great while after the head is cut off, why may not it also actuate parts separated from the body without being extended? On the other hand, if we allow the soul to occupy space, I do not see why it may not continue to be present with the parts of the body after they are separated, as when they were united. And with respect to the divisibility of the soul, which is generally thought to follow from the supposition of its being extended, why may it not be a substance so perfectly and essentially one, as that a division or separation of its parts would necessarily infer a distinction of its essence? Further, if the soul can be present in all, or in any considerable part of the body, at one and the same time, without being discernible, its sphere of existence being so much increased as to act upon the parts when separated will not infer its divisibility. As the Deity is everywhere present, and, in the infinitely distant part of space, actuates at the same time a vast variety of different systems without any inconsistency with his unity or indivisibility; so may not the souls of animals be present everywhere in their bodies, actuating and enlivening at the same time with all their different members? Nay, further, when the fibres and threads connecting some of these parts are divided, may not the soul still act in the separated parts, and yet be only one mind?"

A hundred years later, a vehement advocate of Whytt’s views, Professor Pflüger, deals very boldly with the question which Whytt treats thus tenderly. He undertakes to show "that a kitten, the spinal cord of which is divided, has two souls. For the anterior moiety manifests spontaneous acts of volition, –cries, runs, bites, and scratches; the posterior feels, wills, and moves just as voluntarily. Although both parts exercise their nervous functions in a perfectly independent manner, the rational principles (Vernunft principeen ) are specially present in each, because these are nothing else than functions of the grey matter (Mark function ), and the grey matter in each continues to exert its inherent powers.’

I must confess that to my mind Pflüger’s view is the only logical one, if the hypothesis that the frog has a soul be adopted. A frog’s head is cut off so that the section passes between the medulla oblongata and the rest of the brain. The actions performed by the head and by the trunk will be equally purposive, and equally show that there is a something in each half which possesses the [7] power of adapting means to ends in a manner which is as deserving as the epithet ‘rational’ in the one case as in the other. The separated head and trunk may be sent a hundred miles in opposite directions, and at the end of the journey each will be as purposive in its actions as before. In this case, two alternatives present themselves,–either the soul exists in both cord and brain, or it exists in only one of them.

If we admit the latter hypothesis, it follows that purposive operations may be effected by matter without the help of a soul, –which is a practical acceptance of the automatic doctrine. On the other hand, if we admit the former, then either the soul is indivisible, or it is divisible. If indivisible, it must either be a centre of force, capable of operating on points two hundred miles apart, or it must extend over two hundred miles.

Whichever of these two alternatives be adopted I am unable to see in what respect the soul of the frog differs from matter.

If, lastly, the soul of the frog is divisible, it must needs have extension, and so falls again into the category of matter.

I have not attempted to discuss the question whether the soul of the frog possesses consciousness, because this appears to me to be a totally insoluble problem.

Every one will discover, if he considers his own actions, that he is constantly performing operations directed towards special ends of which he has no consciousness whatever. And therefore it must be granted that it is possible that all the far less complex actions of the frog may be equally devoid of consciousness. Whether they are so or not, is a point on which no positive evidence is attainable, or even conceivable.

1 See the curious essay by Goltz, "Beitage zu Lehre von den Functionen der Nervecentren des Frosches," (1869), and especially the chapter "Ueber den Sitz der Seele des Frosches."

2 Whytt, "Collected Works," p. 200.

3 Vide Gassendi, Dr. Henry More, Sir Isaac Newton, Dr. Samuel Clark, Also, Gassendi's argument, "Obj. contra med. Descartes," p. 32-33.


Any member unavoidably absent from the Meeting can, if he think proper, make written remarks on the foregoing Paper, and forward them to the Secretary. No such remarks should exceed ten minutes in length of delivery viva voce.



1.   THH Publications
2.   Victorian Commentary
3.   20th Century Commentary

1.   Letter Index
2.   Illustration Index

Gratitude and Permissions

C. Blinderman & D. Joyce
Clark University

§ 1. THH: His Mark
§ 2. Voyage of the Rattlesnake
§ 3. A Sort of Firm
§ 4. Darwin's Bulldog
§ 5. Hidden Bond: Evolution
§ 6. Frankensteinosaurus
§ 7. Bobbing Angels: Human Evolution
§ 8. Matter of Life: Protoplasm
§ 9. Medusa
§ 10. Liberal Education
§ 11. Scientific Education
§ 12. Unity in Diversity
§ 13. Agnosticism
§ 14. New Reformation
§ 15. Verbal Delusions: The Bible
§ 16. Miltonic Hypothesis: Genesis
§ 17. Extremely Wonderful Events: Resurrection and Demons
§ 18. Emancipation: Gender and Race
§ 19. Aryans et al.: Ethnology
§ 20. The Good of Mankind
§ 21.  Jungle Versus Garden