rangements may occur in the way of unusual interchanges of nerve fibres.

Chassaignac, and, more recently, Mr. Hilton, in his thoughtful book on "Pain and Rest," have pointed out, as one of the elements of protection to nerves, the fact that in most instances the motor nerves enter their respective muscles on the under side, so that the whole thickness of the muscle is interposed between the nerve and the exterior sources of injury. We may add that on their first entrance to a limb, the larger nerves lie in the leg at the back, or in the arm, upon the inside, where they are singularly secure from harm,

CHAPTER III.

NEURO-PHYSIOLOGY.

Varieties of nerves.-The nerves which connect a limb with the centres fulfill the following functions: They convey outwardly motor impressions, resulting in voluntary or involuntary motion, as the case may be. They carry centripetally the myriads of impressions which constitute sensations, or which, unfelt as sensations, are excitomotory in purpose. Lastly, a system of nerves, known as sympathetic, exercises control over the flow of blood to the tissues. Section of these nerves paralytically dilates the vessels; galvanization contracts them. This system originates in the spinal cord, but there is also evidence that certain spinal nerves, unrelated to the sympathetic, possess the power to cause directly enlargement of arterioles and increase of vasal supply.

Through this compound group of nerves occur such nutritive changes as depend on increased or lessened flow of blood, but these are insufficient to account for all the trophic changes which we witness from disease or injury; and hence has arisen the belief that there are also trophic nerves proper, which, apart from variable blood supplies, or in connection with these, bring about in the tissues alterations, examples of which I shall have to point out from time to time.

In connection with nerve wounds and their consequences, we have to deal with alterations due to the destruction or irritation of the various fibres of nerves

which minister to pain, touch, the thermal sense, motion, calorification, and nutrition.

I do not think it desirable to enter as largely into these subjects as they would be dealt with in a physiological treatise, but I cannot avoid some reference to such portions of their physiology as either aid us to comprehend and relieve nerve wounds, or as are set in new or clearer light by the phenomena of these accidents.

Trophic nerves.-The question which most often presents itself for answer to the neuro-pathologist is as to the existence or non-existence of nerves directly affecting the nutrition of the tissues, apart from the changes induced in them by the section or irritation of vaso-motor nerve fibres. Without attempting to treat fully of this matter, for which, indeed, the physiological groundwork is still deficient, I shall content myself with stating the impressions in this direction which a large experience of nerve wounds has left upon my mind.

When the physiology of the vaso-motor nervous system was first elucidated by the labors of Bernard, Brown. Séquard, Schiff, and others, it was supposed that it would enable us readily to explain the many obscure phenomena which arise out of nerve wounds; but despite the able arguments of Handfield Jones* and some other observers, this hope has gradually faded away, and it is now generally admitted that we must seek elsewhere for a satisfactory explanation of the facts in question.

The effects of injuries or sections of these nerves can be only to cause either contraction or dilatation of vessels, or to put a stop to the pulsatile movements which have been seen in minute vessels in many parts of the animal economy. These alterations, with the consequent changes in blood supply which they bring about, may be direct

*St. George's Hospital Reports, 1868, p. 89 et seq.

results of nerve lesions, or may be caused after partial nerve lesions by reflex influences originating in the wound. No matter how caused, they are limited to too large or too small a supply of blood, or to alternations of these conditions.

To test the probability of the competency of vaso-motor changes to cause the multiplied lesions which follow wounds. of the nerves of the limbs, we naturally turn to the simpler case of injuries of the sympathetic in the neck.

Section of this nerve merely increases the amount of blood which flows in any given time through the tissues in which it is distributed, and also causes a rise in their temperature. But these changes are not permanent, and neither do we find that the face, for example, is then subject to spontaneous inflammations or to other trophic alterations unless the animal be in bad health. Thus, in rabbits long kept confined, I have frequently seen inflammation of the conjunctiva and cornea follow such sections, but not in their more vigorous companions, and such was also Bernard's experience. Moreover, artificial lesions in the latter class appear to heal with unusual celerity.

Like Weber, I have made many attempts to bring about trophic changes in the face by irritating and partially wounding the sympathetic, but my efforts have uniformly failed; nor have like experiments, such as Lister's, upon the sympathetic nerves in the limbs of the frog, been any more fortunate.

Of course, section of these nerves in their course through the compound nerves of the limbs of man is not without indirect influences on the life of the tissues, but unhappily we need as yet early thermometric observations after nerve wounds of the extremities to complete their history.

In speaking of the effect of nerve wounds on temperature, I shall again approach this subject. At present it is only necessary to say that at remote periods after total

sections of nerves in a limb, there are usually lowered temperature and a condition of passive congestion, while the still more remote future affords some evidence of greatly lessened blood supply; the reasons for which changes are not very difficult to trace. Under these circumstances the life of the limb is lowered and exposed parts are easily injured; but repair, though sometimes slow, still occurs, and may even be unusually rapid.

I have watched many such cases of complete separation of a limb, or parts of a limb, from all neural influence, and have failed to see any inevitable consequence except general atrophy, with usually muscular contractions, and a sallow, unhealthy look of the skin, which is apt to become scaly and rough. The nails grow as usual, perhaps a little more slowly, and the hair is commonly unchanged.

Now and then I met with one of these cases in which whitlows occurred, or ulcers formed on parts which either were or were not exposed to mechanical injury. In most instances these ulcers healed easily, in some cases with unusual facility. We can only conclude from these facts that a certain individuality of cell-life controls the results, and that the cell-life of one man so differs from that of another as thus to present us with varied phenomena under what seems to be equality of conditions. At all events, here, if in any case, we have total vaso-motor palsy, and for a long while, at least, probably an excessive blood supply, but no constant symptom save atrophy, and in no case hypertrophy. But atrophy may, and does, take place from nerve injury without notable changes of temperature, so that we are by no means justified in considering this the only constant result of total nerve section, as due to vaso-motor palsy.

After partial nerve wounds there may be contraction of vessels from direct irritation, or reflectively produced dilatations or contractions. I believe that I have seen