examination, the slight resistance encountered being sufficient By J. HERBERT PARSONS.

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1 PROCEEDI NGS OF THE PHYSIOLOGICAL May 10, SOCIETY, A method of measuring a visual illusion. By HORACE DARWIN and W. H. R. RIVERS. The instrument we show is designed for the quantitative study of the illusion which depends on erroneous estimation of the lengths of vertical and horizontal lines when compared with one another. The simplest form of the illusion is that in which the lines to be compared form the two sides of a right angle. The instrument consists of a thin board 250 mm. square covered on one side by black cloth. Three small boles are bored through the board and are at the angles of a right-angled triangle with two equal sides. Two pieces of thread pass through the holes and form the two equal sides. The two ends of each piece of thread are connected at the back of the board by two short spiral springs and a small cylindrical piece which forms a handle. The springs keep the threads tight, and if the handle is moved the thread is moved and different parts of it can be made to appear in the front of the board. Part of each thread is white and part is black; when the handle is moved the point on the thread where the white begins and the black ends also moves. The appearance of the front of the board is a black ground with two white lines at right angles to each other on it; the length of each of these lines can be varied at will. The black part of the thread is nearly invisible when lying on the black cloth. The length of the white part of each thread is measured by the graduations on the bevel edge of a wooden scale. This forms a separate piece and is made like a very small T drawing-square; when applied to the board it at once comes into the right position with the zero of the scale opposite the end of the white line and with the edge parallel and almost touching the thread. The illusion is measured by making one of the lines of a given

2 xii PROCEEDINGS OF THE PHYSIOLOGICAL length, say 100 mm., then adjusting the length of the other line by means of the handle at the back till the two white linles appear equal to the eye, and measuring the length of the comparison line with the graduated scale. In addition to its simplicity, the instrument has the advantages that either the horizontal or the vertical line may be uised as the standard; that varying lengths of the standard line may be used and that the threads are adjusted in such a way that no indication is given by the adjusting movement which can influence the process of visual comparison. The error of reading is small compared with the extent of the illusion. The principle of the method can readily be applied to the measurement of other visual illusions. On the rhythm of muscular tremor due nerve. By Dr FRASER HARRIS. to drying of the I desire to record the time-relations of the irregular tremor produced in a muscle by the partial drying of its motor nerve. Muscle observed was frog's gastrocnemius isolated on crank-myograph and " after-loaded " with 5 grms. On merely tapping the nerve lightly with the back of a scalpel, the muscle went into complete tetanus, lasting in one case for 27 seconds, and thereafter began to exhibit the quivering with a rhythm of from 1 to 2-2 per second. There is no question here of the tremor being one comipounded with that of any antagonistic muscle. In a sense, the tremor is a fatigue phenomenon supervening on a period of relatively greater freshness of the myoplasm. Degenerations following lesions of the retina in monkeys. By J. HERBERT PARSONS. The operations were performed upon six monkeys. A Graefe's cataract knife was introduced into the eye about 4 mm. behind the corneo-scleral margin, at either the nasal or temporal side, thus avoiding injury to the ciliary body, and minimising injury to the retina. It was passed across the eye through the vitreous to the opposite side and the retina wounded there to the required extent, the position of the point of the knife being in some cases observed by the ophthalmoscope (direct method). In other cases, the wound was made without ophthalmoscopic examination, the slight resistance encountered being sufficient to show that the retina had been reached. The exact position of the

3 SOCIETY, MAY 10, wound was determined subsequently by ophthalmoscopic examination, and by suitable section of the eye post mortem. The microscopic examination of the wounds will be detailed elsewhere. The lesions varied in extent and direction, but were mostly small (1 to 3 mm. long), usually transverse to the general direction of the nerve-fibres. They were situated: I, in the R. nasal lower quadrant; II and III, in the L. temporal lower quadrant; IV, in the R. temporal quadrants; V, between the disc and the macula, but at a slightly lower level; VI, just below and outside the macula. The animals were killed from a fortnight to three weeks after the injury. Great care was taken to preserve the normal position of the optic nerves. The degenerations were examined by the Busch-Marchi method. The following general statements may be made: (1) The degenerated fibres in the main retain the same position along the whole course of the nerve, i.e., the nasal fibres keep to the inner side of the nerve and the temporal to the outer side. There are usually some outlying fibres degenerated. (2) There are invariably some degenerated fibres in the optic nerve of the opposite side. These vary in number pari passu with the extent of the lesion, and are absent in control preparations. This result, which is difficult to explain, confirms the previous experiments of Usher and Dean on the rabbit by the ordinary Marchi method. These fibres occupy the homonymous side of the opposite nerve, a fact. which is against their being distributed to physiologically corresponding parts of the opposite retina. (3) The fibres from the macular region pass from the temporal side of the nerve anteriorly, towards the centre as they pass back. (4) In all cases there has been degeneration in both optic tracts. The degeneration in the opposite tract in temporal lesions is slight but definite. As far as the method is capable of showing, it consists of very fine fibres. (5) The fibres spread ouit as they pass back in the tracts, and are distributed over their whole area posteriorly. Most go to the external geniculate body, some to the optic thalamus, and a few to the superior corpus quadrigeminum. (6) In VI there was distinct degeneration amongst the fibres of the IIlrd nerve. It may be stated that other parts of the brains of these monkeys showed no evidences of degeneration when prepared by the same method..,.

4 xiv PROCEEDINGS OF THE PHYSIOLOGICAL On the Ruffling of Feathers in the Bird. (Preliminary Note.) By J. N. LANGLEY. In a former Note (Proc. Physiol. Soc. Jan. 1902, p. xxxv, this Journal, xxvii.) I pointed out that the depression of the contour feathers over the whole of the body could be brought about in the bird by the sympathetic system; such depression had already been found in the neck and head by Jegorow. I mentioned that occasionally stimulation of the cervical sympathetic in the pigeon caused erection of feathers instead of depression. Since the erection or ruffling of feathers appears to be a voluntary action-the bird often keeping the feathers erect as long as is required for preening-the ruffling has been usually considered to be caused by the striated cutaneous muscles, which commonly form a double layer closely attached to the skin. Although the striated muscles may cause certain movements of the feathers, I find that the erection like the depression is brought about by sympathetic nerve-fibres. The sympathetic penna-erector fibres have the same origin and course as the penna-depressor fibres. The erection is more easily obtained from the spinal cord than from the peripheral nerves, and so far as I have seen more easily in the fowl than in the pigeon. After section of the cervical cord in the anaesthetised animal, there is often rhythmic erection and depression of the feathers; moreover the feathers on the neck may rise, whilst those on the body move closer to the skin, or those on the body may rise whilst those on the neck are depressed. Similar effects may be produced by stimulating the spinal cord. Post-mortem erection of feathers, as well as post-mortem depression, occurs in the fowl, and here again there may be erection of feathers on the neck and depression on the body. Administration of curari in addition to anaesthetics does not essentially alter the results. The feathers have two sets of muscles, erectors and depressors, the number and arrangeinent of these varies, there may be as many as sixteen muscular attachments to a single feather; the muscles run for the most part obliquiely from one feather near its point of exit from the skin to the deeper part or to the papilla end of an adjoining feather. The thoracic vagus ganglion of the bird. By J. N. LANGLEY. Section of the vagus nerve in the neck causes degeneration of nerve-fibres both above and below the point of section. The nerve-fibres

5 SOCIETY, MA Y 10, which degenerate peripherally can be followed into the branches of the nerve below the thoracic ganglion, chiefly to the branch which runs to the cesophagus and abdominal viscera. The fibres which degenerate centrally of the place of section, are, we may conclude, afferent fibres having their trophic centre in the thoracic ganglion of the vagus. This ganglion is then homologous, in part at least, with a spinal ganglion. Stimnulation of the central cut end of the vagus, in deep anaesthesia, causes inhibition of respiration, and primary inhibition followed by contraction of the cesophagus, so that some fibres from the jugular ganglion pass down the trunk of the vagus; they do not all leave it in the upper part of the neck. Effect on the pupil of excision of the ciliary ganglion. (Preliminary Note.) By H. K. ANDERSON. The following are the chief observations which I have made so far. After excision of the left ciliary ganglion and section of the right IlIrd nerve proximally of the ganglion in a kitten, the two pupils were equally dilated until, 8 days later, regeneration occurred on the right side. The r. pupil also continued to be widely dilated in a cat 38 days after division of the r. short ciliary nerves. In these observations, therefore, there was no evidence that the denervated sphincter possessed greater tone than the control sphincter even in very dim light or after section of the preganglionic pupillo-constrictor tract on the control side. Under certain conditions, however, the pupil on the side of the excision was the smaller, e.g. in the second experiment mentioned above the r. pupil was smaller in dim light than the left after the local applicatiorn of eserine to both eyes in equal quantity; and 18 days later the r. pupil was the smaller after the death of the cat. In another cat the 1. pupil immediately after the excision of the 1. ciliary ganglion was very widely dilated, but next day the 1. pupil had become slightly smaller, and in dim light was smaller than the right if the cat became restless under observation: upon the same day after the administration of ether and section of both cervical sympathetic nerves the 1. pupil became a slit, though the light pupil was almost maximally dilated, and for 48 hours after death the l. pupil remained much smaller than the right. The 1. pupillodilatator tract was shown to be intact in this experiment by stimulation of the 1. sympathetic nerve. xv

6 xvi PROCEEDINGS OF THE PHYS. SOC., MAY 10, In other observations also made 2 and 318 days after denervation of the sphincter on one side: the pupil on the side of the lesion was the smaller after the death of the animal, though previously it had been the larger since the denervation. My observations, therefore, suggest that the paradoxical pupilloconstriction seen after excision of the ciliary ganglion is due to increased excitability of the denervated sphincter, the exciting stimuli in the observations given above being alterations in the blood supply, eserine, and probably ether itself. The operations were aseptically performed upon ansesthetised animals; no trophic changes occurred in the eyeball.