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PHYSIOLOGY. 



Special Senses. The cause of the dilatation 

 of the pupil which is produced by stimulating the 

 cervical sympathetic has been the subject of 

 much controversy. The various theories upon 

 it suppose that the dilatation is due to the action 

 of the sympathetic vaso-constrictor nerves, by 

 decreasing the quantity of blood in the iris so 

 that it shrinks, or by a longitudinal contraction 

 of the radial arteries of the iris, dragging the 

 sphincter outward ; that it is caused by the con- 

 traction of radially arranged muscular fibers; or 

 by inhibition of the sphincter muscle ; or, in 

 certain circumstances, to a certain degree, by a 

 relaxation of the ciliary muscle ; or, finally, by 

 the simultaneous action of more than one of 

 these causes. The evidence which has been 

 brought forward in favor of one or other of 

 these theories has not been found by J. N. 

 Langley and H. K. Anderson in any case con- 

 clusive. Reviewing the observations, these au- 

 thors think they show a probability that the 

 sympathetic causes a dilatation of the pupil, not 

 by producing a contraction of the blood vessels, 

 but partly by causing a contraction of the dilator 

 muscle and partly by causing an inhibition of the 

 sphincter muscle. A direct examination of the 

 iris during the stimulation of the cervical sym- 

 pathetic shows that the pupil dilates before the 

 vessels contract ; and assuming that the longi- 

 tudinal muscular coat of the arteries contracts 

 simultaneously with the circular coat, the experi- 

 ment shows that the sympathetic dilatation of 

 the pupil is not due to a contraction of the blood 

 vessels. It can be shown also that some I'adially 

 arranged contractile substance exists in the iris, 

 for when local dilatation of the pupil passes a cer- 

 tain limit the opposite side of the iris is dragged 

 toward the stimulated side. This local dilatation 

 is not produced by an inhibition of the sphincter 

 muscle, for the sphincter muscle can be made to 

 contract at the same time, its contraction being 



freatest at the most dilated portion of the pupil, 

 'urther, stimulation of the sympathetic causes 

 shortening of a radial strip of the iris, isolated 

 from the iris on either side of it, and this short- 

 ening may be obtained before or without any 

 contraction of the blood vessels in it ; and on 

 examining the posterior surface of the iris, small 

 waves of contraction may be seen on its posterior 

 surface when the sympathetic is stimulated. 



From careful studies of the subject Steinach 

 has reached the conclusion that the contraction 

 of the iris when detached from the retina is due 

 to the direct action of light upon its structure. 

 He found that no effect was produced by illumi- 

 nating the peripheral zone of the iris (ciliary re- 

 gion) ; but it was necessary that the light should 

 fall upon the pupillary margin, of which, if only 

 a segment be acted upon, contraction occurs. 

 The contraction still took place when the nerv- 

 ous apparatus of the iris was excluded by the 

 action of atropine. The author demonstrates 

 that the contraction is not due to the influ- 

 ence of the chromatophores, and entertains no 

 doubt that it is really the muscular fibers of the 

 sphincter that are acted upon directly. He has 

 made numerous examinations of these, and finds 

 that in amphibia and fishes they are strongly 

 pigmented. In eyes that have been exposed to 

 the light they are short, thick, and not very well 

 defined; while in animals that have been kept 



in the dark they are slender and sharply con- 

 toured. The author regards the presence of pig- 

 ment in these musculaf fibers as the determining 

 cause of their sensibility to light. The several 

 rays of the spectrum are not all of equal power 

 in causing contraction in the isolated iris. In a 

 comment upon Steinach's paper, Langemlorff 

 remarks that other muscle cells besides those of 

 the sphincter pupilhe possess pigment granules 

 in their interior as, for example, those of the 

 tensor choroide* in mammals. 



It is observed by M. A. Chaveau that if one 

 goes to sleep on a seat placed obliquely in front 

 of a window which allows the light from white 

 clouds to fall equally on both eyes, the colored 

 objects in the room appear illuminated by a 

 bright-green light during a very short interval 

 when the eyelids are opened at the moment of 

 awakening. The phenomenon is not observed 

 except at the moment of awakening from a pro- 

 found sleep. Prom this it is concluded that 

 there are distinct perceptive centers for the 

 green, and probably also for the violet and the 

 red. Of these the green centers are those which 

 first regain their activity on awakening. 



A report was made at a recent meeting of the 

 Vienna Society of Physicians by Dr. Kreidl, an 

 assistant of Prof. Exner, on experiments he had 

 made on deaf mutes concerning the physiology 

 of the labyrinth. Touching the experiments 

 made on this subject by Flourens, Goltz, Mach, 

 and Breur, he pointed out that the membranous 

 canals of the external ear should be regarded as 

 the peripheral part of the mechanism of the 

 sense of equilibrium, the sensations of the dis- 

 turbance which he takes to be produced by the 

 flow of the fluid of the ampulla and in the mem- 

 branous canals. If the views of physiologists on 

 the function of the otoliths and the membranous 

 canals be true, it would have been expected that 

 anomalies of the sense of equilibrium should be 

 found in deaf mutes. Purkinje had previously 

 observed that if a person is made to rotate on 

 his own axis, the eyeballs were moved to the side, 

 as in nystagmus. This, in Dr. Kreidl's experi- 

 ments, was not observed in deaf mutes to any 

 large extent. From other experiments the au- 

 thor was led to regard the otolithic organs as a 

 statical sense. 



From observations made upon a student, twen- 

 ty-one years of age, suffering from complete anos- 

 mia a defect evidently congenital, and inherited 

 from the patient's mother but in whom taste 

 and common and thermal sensibility were undis- 

 turbed, Prof. Jastrow found that the greater 

 number of taste perceptions, as they are com- 

 monly understood, are really to be referred to 

 smell. No distinction could be made by the sub- 

 ject between tea, coffee, and hot water, so that he 

 took the hot water, with sugar and milk, as his 

 ordinary breakfast beverage. He confounded 

 bitter-almond water and water three times in 

 five trials, while he correctly discriminated ether 

 and water, the former, he said, producing in his 

 throat the sensation of peppermint. With am- 

 monia and ether he was right six times in eight 

 trials ; and Prof. Jastrow ascribes the two errors 

 to fatigue. The various fruit sirups he could 

 not distinguish, merely recognizing them as 

 sweet. Mustard produced a sharp sensation on 

 the tongue, but was not re'cognized any more 



