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account of Mr. Clarke's views, we would refer to a paper published by him in 'Beale's Archiv,' and to a recent paper in the Natural History Review,' in which may be found also an abstract of the latest observations. Before leaving the subject of structure, we should like to give the generalization of German observations adopted by Funke in the last edition of his 'Text-book on Physiology.' These

are:

*

"1. The nerve-fibres, which leave the cord in the anterior roots, take their origin in all animals (as in man) in the ganglionic cells, which are placed throughout the whole length of the cord opposite the points from which the roots go off. No root goes direct to the brain without the interposition of a ganglionic cell. This is the most certain result of all observations on the cord, and few will now dispute it. Even Kölliker, who at first stoutly denied this fact, and held that in the human spinal cord the cells were quite isolated, and had no connexion with the root-fibres, is now inclined to believe in the origin of a part of the fibres of the anterior roots in the cells of the anterior horns. I myself have not only in the frog, but also in the cord of the mammal, distinctly observed processes of the ganglionic cells run deep into the white substance, so that I have no doubt as to the above statement; and especially as no observer has been able to follow an isolated fibre through that cell-group into the white substance of the anterior or lateral columns. When we see a root fibre coursing amongst these cells without entering them, it is not at all improbable that the fibre terminates in a cell on a higher or lower level. Still less may one assume with Lenhossék, when we see a fibre apparently end free between the cells, that a free ending occurs in that spot, but must rather suppose that what appears to be the end of a fibre is merely a section of one as it is bending upwards.

"2. All the fibres of the anterior roots stand in mediate connexion with the brain, through the processes issuing from their ganglionic cells into the white substance. As a rule, a great number of root-fibres appear to end in a group of anastomosing cells, from which only one or two channels of communication go off to the brain. The existence of anastomosing systems of nerve-cells in the anterior horns, is, in my opinion, an undoubted fact not only in man and mammals, but also in the cord of the lower vertebrata, as I have convinced myself, contrary to the opinion of Kupffer and Owsjannikow. I have isolated cells from the anterior grey substance of the frog with more processes than the Dorpat school have described, in which some of the processes, more espe cially those which run inwards and backwards, divided in a fork-like manner. I have also most distinctly seen in the frog that the cells were connected with each other. How it happens that such a master of observation as Kölliker has observed no undoubted cell-anastomosis is an enigma. It remains to be proved whether the processes of these anterior cells ever end free.

"3. There is no crossing of the anterior root-fibres in the cord, but a mediate connexion of the anterior roots of both halves of the cord takes place through the anterior grey commissure, which is nothing else but the connecting fibres of the cells of both sides. What Kölliker has taken for a crossing of the anterior columns, and what others hold to be an anterior white commissure, is nothing else than the crossing of the connective-tissue fibres of the pia mater in the substance of the cord, which was first discovered by Arnold, correctedly described by Blattmann, aud particularly so by Kupffer. We shall see that physiological experiment is also opposed to the idea of the crossing of the anterior roots. After several careful examinations of fresh and hardened preparations of the cord of the frog, I have been unable to

Goll, Trask, Reissner, Stieder, Dean, Traugott.

convince myself of the nervous nature of the system of cross fibres behind the anterior fissures.

"4. In regard to the relations of the posterior roots, we have less sure data. Bidder and his pupils hold that in a frog and in a fish all the posterior roots enter the ganglionic cells, from which the anterior roots spring. From my own studies in the subject I am convinced that this is the case with a part of the fibres, but not with all. Certainly, in the higher animals, in which the greater part of the posterior roots does not enter the ganglionic cells, Bidder's idea does not hold. Whether these fibres pass through ganglionic cells in the grey substance, before they pass over into the central channel of the white substance, and whether a crossing takes place behind the central canal, are still undecided questions. Schröder van der Kolk has lately convinced himself of the ending of the sensitive root-fibres in ganglionic cells of the posterior horn, and supposes that the farther conduction of impressions proceeds to the other side, and in this to the brain. He bases this supposition also on the analogy of the sensitive nerves which terminate in the grey nuclei of the medulla oblongata. The existence of a posterior grey commissure, and its importance as a cross-passage of the posterior nerve-roots, I hold as very probable; and I believe it occurs even in the frog, as Kölliker and others have lately testified. From a physiological point of view, the existence of fibres which go to the ganglionic cells of the anterior roots as the direct passage the greater part of the posterior root-fibres in their passage to the brain, and, finally, decussation of the posterior root-fibres, may be supposed. A direct transition of the posterior root-fibres into the anterior I hold as improbable.

of

"5. The longitudinal fibres of the white substance come collectively out of the grey substance, and represent mediate or immediate continuations of the anterior and posterior root-fibres. All processes of the first rise from the ganglionic cells of the anterior grey substance in which the anterior root-fibres originate. How far the continuations of the posterior nerve root-fibres communicate directly, or through the medium of cells, with these fibres, is yet to be ascertained.

"6. The grey substance consists of a stroma for ganglionic cells, in which these connect themselves with root-fibres or with each other. It is doubtful whether in the grey substance nerve-fibres exist which are not related to its ganglionic cells."

In connexion with the structure of the spinal cord, we would refer to a very interesting paper by Dr. T. S. Clouston on the Minute Anatomy and Physiology of the Nervous System in the Lobster.' In this animal it is found that, in every essential point, the ganglia and interganglionic cord correspond to the spinal cord of the vertebrate animal. The origin of fibres from cells, the connexion of cells with each other, a connexion between the various groups of cells in different ganglia, and a correspondence between the number of ganglionic cells and that of the muscles which they minister to, are facts (Dr. Clouston shows) equally susceptible of confirmation in the invertebrate as in the vertebrate class of animals.

In analysing recent observations on the function of the spinal cord, it will be convenient to regard the organ in a three-fold character : 1st, as a centre for the reflection of impressions made on its afferent nerves; 2nd, as a sensorial centre; 3rd, as a conducting organ.

I. The spinal cord is a reflecting centre-i.e., an organ capable of converting impressions made on its afferent nerves into motor impulses, without and independent of the co-operation of the will. One

of the earliest to perceive this fact was Prochaska, but it was left for our distinguished countryman, Marshall Hall, to indicate the importance and to explain the conditions of the reflex endowments of the spinal cord. Since his time (1833-43) the subject has been specially considered by Müller (1834); Volkmann (1838); Valentin (1839); Arnold (1842); Grainger (1837); Spiess (1844); Weber, Wagner (1854); and last, but not least, by Edward Pflüger (1853).

The study of reflex action can be conducted only under circumstances in which the influence of the will is excluded. Accepting the conclusion that the brain is the exclusive organ of the psychical functions; that in it only occurs perception of sensitive impressions (sensation); that from it alone proceeds the influence of the will, it would follow that all the motions produced in a decapitated animal were of a reflex character. But this conclusion has not only been doubted, but strenuously denied; and in the modern text-books of physiology we meet with the query, 66 Sensorium im Rückenmark?" A little

consideration of this question may interest the reader.

In 1853, Pflüger published a work* in which it was contended, from experiments on animals, that the spinal cord is the seat of sensorial functions. In earlier times this idea was hinted at, and even distinctly indicated, by Prochaska, Legallois, Cuvier, and Volkmann. One of Pflüger's most striking experiments is the following: a frog is decapitated, and acetic acid is placed just over the internal condyle of the femur. The animal constantly bends the limb, and with the dorsal surface of the foot of the same side wipes off the acid by alternate movements of ad- and ab-duction. This we have often seen. The foot is now cut off, so that "wiping" is no longer possible, and the acid is reapplied. The animal bends the thigh as formerly (for it still supposes it possesses its foot), but it soon gives up this movement, becomes restless "as it seeks after a new method," and finally using the limb of the other side, bends it, so that by the sole of the foot the acid is removed. If other modes of irritation are employed, the movements which follow are said always to present an appearance of purposiveness (Zweckmässig keit).*

But mere purposiveness of action would not prove the existence of psychical activity in the cord, for are not all reflex arrangements purposive in their object? We must look to some other characteristic. Supposing that each sensitive fibre is connected mediately with a system of motor fibres, so that the former may, when excited, call forth a determined harmonious muscular action (such as the will would call forth), then we must expect that the action called forth by the excitation of a centripetal fibre must always be the same when the exciting agent is similar, and applied under the same conditionsin fact, with such a mechanical arrangement as we have supposed, we would expect a degree of regularity in the results of au excitation. It is urged by those who contend for the sensorial functions of the cord,t

Die sensorische function des Rückenmarkes der Wirbelthiere nebst einer neuen Lehre über die Leitungsgesetze der Reflexionen. Berlin, 1853.

Pfluger, Funke, Auerbach.

that a different reaction is observed when different modes of irritation are employed, and that each reaction is purposive in relation to the excitant. For instance (say they), if we pinch the thigh of a decapitated frog at a certain spot, he will either draw up the limb energetically, and place it under his belly, or he will stretch the limb as if to push away the instrument; or, if the medulla oblongata is retained, he will hop away. If instead of pinching this same spot we apply strong acetic acid, none of these movements follow, but the animal, by a to-and-fro movement of the foot of the same or of the opposite side, contrives to wipe off the offending acid. Now, supposing this experiment to be true to the letter, it might be urged that even with a determinate reflex mechanism different irritants might call forth different muscular actions. However, if this experiment gives results as decided as those just mentioned, we think it difficult to imagine such a possibility; for if the resulting muscular movements depend upon the construction of a mechanism, one of the limbs of which goes to the part at which our excitant is applied, it is scarcely probable that the play of this mechanism will be different (to the extent implied in the experiment) when the nature of the exciting application is different. In a former paper* we showed that, in their effect on the molecular mechanics of the nerve-fibre, chemical and mechanical excitation acted alike. Those who have had experience in such experiments say that a decapitated frog does not always act in the same way when acetic acid is applied to his thighs, but that it now adopts one expedient to remove the acid, now another. The first experiment we quoted shows a degree of accommodation to circumstances which can with difficulty be explained by the supposition of a reflex mechanism.

These experiments on decapitated frogs are certainly curious and interesting, but we must remember that their aim is to establish the possession of faculties purely subjective in character. They attempt to prove that animals far removed from man, and deprived of their brains, and consequently of the organs of special sense, are capable of sensation (consciousness of sensibility), perception of external conditions, and of adaptation of means to an end. The latter, of course, implies the exercise of what in the frog must constitute the highest psychical faculties. All these matters are of a subjective character. We suppose that another man feels the same degree and character of pain as we do when a needle is pushed into his skin; but we cannot prove it, much less can we dogmatize on the feelings of a decapitated frog. On the other hand, it appears to us worthy of remembrance that in fish and frogs anatomical observers (Kupffer and Owsjannikow) have pointed out that both sensitive and motor fibres of the cord arise from one and the same nerve-cell, suggesting a generalization of function. Does not this fact somewhat harmonize with Pflüger's experiments? Profesor Schiff, whose opinion on neurological subjects is of the highest value, winds up a searching criticism on the sensorial functions of the cord with the following conclusions:

* On General Nerve Physiology: British and Foreign Medico-Chirurgical Review, July, 1862.

"1. There is no reason why we should deny to the spinal cord of an animal recently decapitated the faculty of sensation.

"2. It is rather highly probable that in such a cord true sensation occurs after irritation.

"3. The fundamental principle, by which sensitive impressions become converted into movements, is the same in the brain and spinal cord.

"4. The spinal movements are distinguished from the cerebral essentially in this, that in the latter, as Cuvier indicated, the central spheres of the higher organs of sense (sight, hearing, perhaps also smell) co-operate in themselves and on the motory nerves, as reflecting excitants. It must, therefore, appear that the withdrawal of these centres must have a most important influence on the whole character of the motory and sensational functions of the spinal cord."*

The idea of consciousness and volition being present in the spinal cord Schiff entirely renounces, and he regards all the movements of decapitated amphibiæ as the mechanical consequences of irritation of a nervous reflecting organ. The operation of the irritant he believes to be determined by its strength, not by its character.

On the other hand, Funke avers that, "according to his opinion, from a purely physiological stand-point, the spinal cord possesses sensorial functions." The real difficulty of the question seems to consist in this, that we at present possess no certain indication by which movements of a reflex character-(i.e., purely mechanical), can be distinguished from those originated by a psychical impulse. Accordingly, any attempt to determine the laws of reflex action must prove unsatisfactory.

In the work of Pflüger to which we have referred, such an attempt has for the first time been made; and as his results are in part founded on an analysis of pathological observations on man, an account of them may interest the reader. They are shortly as follow:

1. The law of conduction on the same side for one-sided reflection. If, on irritation of a sensitive nerve, reflex action follows on one side only, the latter occur without exception and under all circumstances on that side only which corresponds to the irritated sensitive nerve. This law was recognised by John Müllar.

2. The law of symmetrical reflection. If a sensitive irritation has produced reflex movements on one side, and by further extension has aroused motor action also on the other half of the cord, only those nerves will be affected which correspond to those originally irritated on the first half.

3. The law of unequal intensity of reflex action on both sides of the body in double-sided reflexes. When double reflex occurs, it is always strongest on the side corresponding to the sensitive fibre irritated.

4. The law of intersensitive-motor movement, and of reflex irradiation. By the first term Pflüger understands the channel by which the irritation travels from the sensitive to the motor fibres, in the central organ. By the latter term he understands the further progress of reflex action from the nerves in which it was localized to neighbouring nerves. If the excitation of a sensitive cerebral nerve is transferred to motor

* Lehrbuch, p. 221.

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