medium, work done on a moving mirror, and the laws of reflexion and refraction as modified by motion, are considered.

It is found that the law of reflexion is not really obeyed in a relatively moving medium, though to an observer stationary with respect to the mirror it appears to be obeyed, so far as the first order of aberration magnitude is concerned; but that there is a residual discrepancy involving even powers of aberration magnitude, of an amount possibly capable of being detected by very delicate observation.

The following statements are made and justified :

(1.) The planes of incidence and reflexion are always the same. (2.) The angles of incidence and reflexion, measured between ray and normal to surface, usually differ.

(3.) If the mirror is stationary and medium moving, they differ by a quantity depending on the square of aberration magnitude, i.e., by 1 part in 100,000,000; and a stationary telescope, if delicate enough, might show the effect.

(4.) If the medium is moving and mirror stationary, the angles differ by a quantity depending on the first power of aberration magnitude (1 part in 10,000), but a telescope moving with the mirror will not be able to observe it; for the commonplace aberration caused by motion of receiver will obliterate the odd powers and leave only the even ones; the same as in case (3).

(5.) As regards the angles which the incident and reflected waves make with the surface, they differ in case (3) by a first order magnitude, in case (4) by a second order magnitude. (6.) At grazing incidence the ordinary laws are accurately obeyed. At normal incidence the error is a maximum.

(7.) The ordinary laws are obeyed when the direction of drift is either tangential or normal to the mirror; and are disobeyed most when the drift is at 45°.

(8.) In general, the shape of the incident wave is not precisely preserved after reflexion in a moving medium. To a parallel beam the mirror acts as if slightly tilted; to a conical beam as if slightly curved. But either effect, as observable in the result, is almost hopelessly small.

(9.) Similar statements are true for refraction, assuming Fresnel's law.

The possibility of obtaining first order effects from general ethereal motion by means of electrical observations is considered.

V.The Abductor and Adductor Fibres of the Recurrent Laryngeal Nerve." By J. S. RISIEN RUSSELL, M.B., M.R.C.P. Communicated by Professor V. HORSLEY, F.R.S. Received March 17, 1892.

(From the Pathological Laboratory of University College, London.*)

I. Introduction.

CONTENTS.

II. Historical Account of Previous Experimental Researches.

III. Operative Procedure.

IV. Division of Subject and Analysis of Results.

A. Division of the Subject.

B. Analysis of Results.

Section 1. Separation and Excitation of the Individual Bundles of which the Nerve is composed.

Section 2. Relative Vitality of the Respective Bundles.

Section 3. (Control) Tracing the Respective Bundles to their Peripheral Terminations by Dissection.

Section 4. (Control) Direct Observation of the Abductor and Adductor Muscles in Action after Dissection.

Section 5. (Control) Degeneration Method.

V. Summary and Conclusions.

INTRODUCTION.

While engaged in certain experimental investigations in connexion with the cervical nerve roots of the dog (Roy. Soc. Proc.,' 1892), the ease with which I found one could separate, in a nerve root, the different bundles of nerve fibres which are concerned with one function from those concerned with another, or even a bundle of nerve fibres destined for the supply of one muscle from one destined for the supply of another, led me to suppose that by exercising sufficient care, it might be possible to separate, in the same way, the abductor from the adductor fibres in the recurrent laryngeal nerve. It is a matter of clinical and pathological experience (Semon, Rosenbach) that in organic and progressive affections of this nerve the abductor fibres are prone to succumb before the adductors; but why this should be so is not at all clear. In like manner, in the wellknown experiments of Gad and B. Fränkelt on freezing the nerve, the abductor fibres give way before the adductors do. Jeanselme and Lermoyez, by electrical excitation of the laryngeal muscles of human

Part of the expenses connected with this experimental research have been defrayed by a grant from the Scientific Grants Committee of the British Medical Association.

+ Centralblatt für Physiologie,' May 11, 1889.

subjects who died of cholera, found that the crico-arytenoideus posticus muscles were the first to lose their excitability after death. This observation has been abundantly confirmed by Horsley and Semon for all classes of animals. On the other hand, ether, reaching the laryngeal muscles through the circulation, puts the adductors into abeyance before the abductors, so that, while excitation of the recurrent nerve of an animal not very deeply under its influence results in adduction of the corresponding vocal cord, similar excitation of the nerve when the animal is profoundly under the influence of the anaesthetic results in abduction of the cord.† It seemed, therefore, not unlikely that, if the fibres dominating over the one function could be successfully separated from those dominating over the other, some fresh light might be thrown on this subject.

It is interesting to find that Dr. Felix Semon,‡ in a paper written so long ago as 1881, asked the following question with regard to the fibres of the recurrent laryngeal nerve: "Are we to suppose that, though the nerve is apparently homogeneous, it consists in reality of a bundle of strictly differentiated fibres, bound together simply by a common nerve sheath, and actually differentiated throughout their peripheral course; in fact, having ganglionic centres of their own? Dr. Semon then goes on to show that the pathological facts strongly support the probability of the truth of this hypothesis.§

Morell Mackenzie,|| in his text-book published the year before Semon raised this question, suggested that possibly the abductor filaments were more superficially situated than the adductor fibres, and that this, if true, would account for the proneness of the abductors to succumb before the adductors in affections, especially compression by tumours, of the nerve. There is, however, no ground for this hypothesis.

Since then, the general question of the proclivity of the abductor fibres has been the subject of great controversy, and has been debated both from a clinical and pathological standpoint, but, so far as I am aware, very few attempts have been made to determine

'

* British Medical Journal,' Aug. 28 and Sept. 4, 1886.

Hooper, Trans. of the Amer. Laryngol. Assoc.,' vol. 7; Horsley and Semon, 'British Medical Journal,' Sept. 4 and 11, 1886.

Semon, Arch. of Laryngology,' 1881, vol. 2, p. 200.

§ Dr. Semon's views have been amply confirmed by direct experiments on the cortical and bulbar centres for the laryngeal muscles. See history of the subject in paper by Semon and Horsley, Phil. Trans.,' 1890.

Mackenzie, A Manual of Diseases of the Throat and Nose,' 1880, vol. 1,

p. 440.

For a full history of this, see Semon's contribution to the Virchow-Festschrift'; "Die Entwicklung der Lehre von den motorischen Kehlkopflähmungen seit der Einführung des Laryngoscops," 1891.

the arrangement of the fibres in the trunk of the recurrent laryngeal nerve, either by anatomical observation or direct experimental investigation.

HISTORICAL ACCOUNT OF PREVIOUS EXPERIMENTAL RESEARCHES.

*

Hooper, wishing to decide, by experimental investigation, whether it is the abductor or the adductor fibres that are really the more prone to succumb in affection of the recurrent laryngeal nerve, passed a thread through the middle of one recurrent nerve, and left it in situ in the hope that it would act as a foreign body and excite inflammation of the nerve. At the end of a week, on inspecting the larynx, the vocal cord on the side corresponding to the injured nerve was observed not to come up to the middle line with the same "snap " on expiration as did the cord of the opposite side.

The nerve was found imbedded in a mass of inflammatory tissue, and electrical stimulation of its trunk below this point resulted in abduction of the corresponding vocal cord. When a strong current was used, stimulation of the nerve resulted in abduction of the vocal cord of the same side, and adduction of that of the opposite side. The opposite uninjured nerve was next divided, and adduction of the vocal cord on this side followed stimulation of its peripheral end. Division of the injured nerve below the point at which the thread had been inserted, and stimulation of its peripheral end, resulted in distinct outward rotation of the arytenoid cartilage of that side and an approximation of both arytenoid cartilages at the same time. All attempts to verify these results have failed, so that the experiment stands alone. Proneness of the adductors to suffer before the abductors is what this experiment seemed to point to, but the observer was unable to lay very great stress on this single experiment, positive as it seemed.

The possibility of direct injury to the adductor fibres during the process of inserting the thread into the nerve does not seem to have occurred to this observer, a possibility which is more than likely. Further, it is quite evident that the effects he obtained on the opposite cord, by stimulating the injured nerve, were due to diffusion of the electrical current to the nerve of the other side by diffusion to the vagal trunk, and so reflexly to the opposite nerve.

Onodit exposed the muscles of the larynx in dogs, and found that at the point where the recurrent laryngeal nerve crosses the cricoarytenoideus lateralis muscle it splits into three bundles, the first of which supplies the crico-arytenoidens posticus, the second the arytenoideus transversus and crico-arytenoideus lateralis, and the third * Hooper, New York Med. Journ.,' July 4, 1885. + Onodi,

Berliner Klin. Wochenschr.,' 1889, No. 18.

the thyro-arytenoideus externus. He passed a ligature round each branch, divided all three branches, and then stimulated each separately by an electrical current, and noted the movements of the vocal cords. The communication is an exceedingly brief one; but the observer promised to publish a full account of his experiments later. As far as I am aware, no such publication has appeared up to the present.

These observations can scarcely be said to have thrown much fresh light on the question at issue, as it is only natural to suppose that this nerve, in common with all other motor nerves, should so near its peripheral termination divide into several branches, and that stimulation of each branch of the nerve should evoke contraction of the muscle which it supplies, and thus bring about the particular movement of the vocal cord over which the muscle presides. But this does not at all decide the all-important question as to whether the nerve fibres presiding over the different functions have a separate course throughout the entire length of the nerve trunk or not.

Dionisio* performed tracheotomy, and then inserted a laryngeal "dynamometer" between the cords. This consisted of a small indiarubber ball, which communicated by means of a tube with a mercurial manometer. The height of the mercurial column during inspiration and expiration was then noted during the natural movements of the vocal cords, its position during expiration being of course higher than during inspiration. The recurrent laryngeal nerve was exposed and stimulated with an electrical current sufficiently strong to produce moderate adduction of the corresponding vocal cord, during which the mercurial column rose. When excitation was discontinued it fell again, and oscillated between the two former points. Circular pressure was then applied to the nerve, commencing with 5 grammes, and going up to 350 grammes, by gradual stages; pressure being kept up for 2 minutes at each stage. It was found that on stimulating the nerve after each stage there was a gradual diminution in its power of conduction, until stimulation on the proximal side of the point of pressure no longer gave any response, while stimulation on the distal side resulted in a rise of the pressure, but not nearly so great as formerly. There was a gradual fall of pressure, the inspiratory and expiratory preserving about the same ratio. they bore to each other before the pressure was commenced.

OPERATIVE PROCEDURE.

Dogs were without exception the animals used in these experiments, and in every case ether narcosis was produced and continued throughout the whole course of the experiment, at the end of which the animal was always killed by an overdose of the narcotic, except in

* Dionisio, Arch. Italiani di Laringol.,' January, 1892, p. 1.