moved. This mass had the consistence of the white substance of the brain, and presented a perfect continuity with the cerebral peduncles, which had not been removed. It had the form of the two hemispheres, presenting a cavity filled with liquid and a septum. The whole mass consisted of perfect primitive fibres of double contour, and, in their meshes, ganglionic cells.'

This observation is certainly one of the most remarkable on record, and, from the extraordinary character of its results, would hardly be accepted for a moment, but for the established reputation of Prof. Voit. As it is, such an observation demands full confirmation. It is well known to all who have been in the habit of removing the cerebral lobes, that it is absolutely necessary to remove every portion of their substance, in order to obtain uniform results, and that this is accomplished sometimes with considerable difficulty. In demonstrations to a medical class, we have frequently verified this fact, and have observed recovery, more or less complete, when but a small portion of the posterior lobes escaped. This criticism upon the remarkable observation just detailed is made by Vulpian,' and its pertinence will be recognized by every practical physiologist. We have only to study the experiments first made by Flourens, to learn how, in the lower animals, a part of one of the great central ganglia may gradually assume the function of the whole, after this function has been interrupted by the first mutilation."

We have cited the essential points in this observation because it has been so extensively commented upon by physiologists, but it is far from establishing the principle that a great nervous centre, like the cerebrum, may be anatomically and functionally regenerated after extirpation.

1 C. VOIT, Phénomènes qui suivent l'ablation des hémisphères du cerveau chez les pigeons (Académie des Sciences de Munich), traduit de l'allemand par le Dr. RABUTEAU.-Revue des cours scientifiques, Paris, 1869, tome vi., p. 256.

* VULPIAN, Archives de physiologie, Paris, 1869, tome ii., p. 302.

3 FLOURENS, Recherches expérimentales sur les propriétés et les fonctions du système nerveux, Paris, 1842, p. 100.

The general results of the experiments of Masius and Vanlair upon the regeneration of parts of the spinal cord in frogs, after loss of a small portion of its substance, show that such reparation may take place and is attended with restoration of function. The formation of cells precedes the development of fibres, and voluntary motion appears in the parts situated below the lesion, before sensation. There are no instances on record of such regeneration in the human subject or in the warm-blooded animals.

1 MASIUS ET VANLAIR, Recherches expérimentales sur la régénération anatomique et fonctionnelle de la moelle épinère, Bruxelles, 1870.

CHAPTER II.

MOTOR AND SENSORY NERVES.

Distinct seat of the motor and sensory properties of the spinal nerves-Speculations of Alexander Walker-Views of Sir Charles Bell regarding the func tions of the anterior and posterior roots of the spinal nerves-Experiments of Magendie on the roots of the spinal nerves-Properties of the posterior roots of the spinal nerves-Influence of the ganglia upon the nutrition of the posterior roots-Properties of the anterior roots of the spinal nerves— Recurrent sensibility-Mode of action of the motor nerves-Associated movements-Mode of action of the sensory nerves-Sensation in amputated

members.

THE physiological property of nerves which enables them to conduct to and from the centres the impressions, stimulus, force, or whatever the imponderable nervous agent may be, is one inherent in the tissue itself, belonging to no other structure, and is dependent for its continuance upon proper conditions of nutrition. So long as the nerves maintain these conditions, they retain this characteristic physiological property, which is generally known under the name of irritability.

Aside from the special senses, the sense of temperature, and of weight, it is known to every one that through the nerves we appreciate what are called ordinary sensations, and are enabled to execute voluntary movements. If a nerve distributed to a part endowed with sensation and the power of motion be divided, both of these properties are lost, and can only be regained through a reunion of the divided nerve. Again, it is equally well known that if such a nerve be exposed in its course and irritated, violent movements take place in the muscles to which it is distributed, and pain is appreciated, referred to parts supplied from the

same source. These facts, which were fully appreciated by the ancients, show that the general system of nerves is endowed with motor and sensory properties, the question being simply whether these be inherent in the same fibres or belong to fibres physiologically distinct and derived from different parts of the central system. This question, which was solved only about half a century ago, will be the first to engage our attention.

Distinct Seat of the Motor and Sensory Properties of the Spinal Nerves.-All of the nerves that take their origin from the spinal cord are endowed with motor and sensory properties. These nerves supply the whole body, except the head and other parts receiving branches from the cranial nerves. They arise by thirty-one pairs from the sides of the spinal cord, and each nerve has an anterior and a posterior root. The anatomical differences between the two roots are that the anterior is the smaller, and has no ganglion. The larger, posterior root presents a ganglionic enlargement in the intervertebral foramen. Just beyond the ganglion, the two roots coalesce and form a single trunk. The nerve-fibres in the two roots are not of the same size, the anterior fibres measuring on an average about one-fourth more than the posterior fibres.' The structure of the ganglia of the posterior roots has already been considered sufficiently in detail.'

It would be unprofitable to discuss the vague ideas of the older anatomists and physiologists with regard to the properties of the roots of the spinal nerves, and we can date our information upon this point from the suggestion of Alexander Walker, in 1809, that one of these roots was for sensation alone and the other for motion. It is most remarkable, however, that Walker, from purely theoretical considera1 KÖLLIKER, Éléments d'histologie humaine, Paris, 1868, p. 339.

* See page 51.

3 WALKER, New Anatomy and Physiology of the Brain in particular and of the Nervous System in general.—Archives of Universal Science, Edinburgh, 1809, vol. iii., pp. 173, 174.

tions, should have stated that the posterior roots were motor and the anterior roots sensory, precisely the reverse of the truth, and should have advanced this view in a publication as late as 1844.' In the work alluded to, which contains. some of the most extraordinary pseudo-scientific vagaries ever published, it is curious to see how near Walker came to the greatest discovery in physiology since the description of the circulation of the blood. He gives an account of an experiment as follows: "On opening the spinal canal of a frog, accordingly, and performing the only operation on a living animal which he ever has performed, or ever will perform, he found that, in perfect conformity with previous reasoning, irritation of the anterior roots caused motion, and irritation of the posterior roots caused little or none." " Now, it does not appear in the work from which this quotation is made at what time this experiment was performed; and we have not been able to ascertain that it was done before 1811; but, correctly interpreted, this observation had been almost the great discovery. To conclude our review of the claims of Walker, there can be no doubt of the fact that he was the first to distinctly assign motion and sensation to the different roots of the spinal nerves, though he incorrectly ascribed motor properties to the posterior roots and sensory properties to the anterior, and brought forward not one iota of proof in support of his theories.

The claims of Mayo to the discovery of the distinct properties of the roots of the spinal nerves are very indefinite. He simply states, long after the publication of the experiments of Magendie, that the "remarkable analogy which exists between the fifth nerve and the spinal nerves

1 WALKER, The Nervous System, anatomical and physiological: in which the functions of the various parts of the brain are for the first time assigned, and to which is prefixed some account of the author's earliest discoveries, of which the more recent doctrine of Bell, Magendie, etc., is shown to be at once a plagiarism, an inversion, and a blunder, associated with useless experiments, which they have nei ther understood nor explained, London, 1844, p. 50, et seq.

WALKER, op. cit., p. 18.