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Show 172 EXPRESSION OF SUFFERING : CHAP. VI. rnation. Finally, there nrc numerous mo1·bid states an(l structural alterations of the eyes, and even terrible inflammations, which 1nay be atten(1ed with little or uo srcr tion of tears. It also deserves notice, as indirectly bearing on our subject, that the eye and adjoining parts are subject to an extraordinary nu1nber of reflex and associated movenlents, sensations, and actions, besides those relating to the lacrymal glands. When a bright light strikes tho retina of one eye alone, the iris contracts, but the iris of the other eye moves after a 1neasurable interval of tilne. The iris likewise 1noves in accommodation to near or distant vision, and when the two eyes are 1nado to converge.23 Every one knows how irresistibly the eyebrows are drawn down under an intensely bright light. The eyelids also involuntarily wink when an object is move<I near the eyes, or a sound is suddenly heard. The well-known case of a bright light causing some persons to sneeze is even more curious ; for nerveforce here radiates from certain nerve-cells in connection with the retina, to the sensory nerve-cells of the noRe, causing it to tickle; and from these, to the cells which co1nmand the various respiratory muscles (the orbiculars included) which expel the air in so peculiar a 1nanner that it rushes through the nostrils alone. To return to our point: why arc tears secreted during a screa1ning-fit or other violent expiratory efforts? As a slight blow on the eyelids causes a .copious secretion of tears, it is at least possible that the spasmodic contra tion of the eyelids, by· pressing strongly on tho eyeball, should in a similar uutnner cause some secro- 23 S o, on these sevorn.l points, Prof. Donllcrs 'On t.he Anomalies of Accommodation and Refraction of the Eye,' l8G4, p. 573. CrrAP. VI. 173 tion. This seen1s possible, although tho voluntary contraction of the same muscles does not produce any such e!lect. We know that a man cannot voluntarily sneeze oe cough ~with nearly the same force as he does automatically; and so it is 'vith the contraction of tho orbicular 1nuscles : Sir 0. Bell experi1nented on thotn, and found that by suddenly and forcibly closing the eyelids in the dark, sparks of light are seen, like those cau eel by tapping the eyelids with the fingers; " but in sneezing the compression is both more rapi<I " and 1nore forcible, and tho sparks are more brilliant." That these sparks are dne to the contraction of the eyelids i clear, b cause if they "aro held open during " the act of sn ezing, no sensation of light will bo " experi need." In tho peculiar cases referred to by Prof sor Donders and Mr. Bowman, we have se n that some weeks after the eye has been very slightly injured, spasmodic contractions of the eyelids onsup, and these are accompanied by a profuse flow of tear·. In the act of yawning, the tears are apparently duo solely to the spasmodic contraetion of tho 1nusclcs round the eyes. Notwithstanding these latter cascH, it e tns har lly credible that the pressure of the eyelid~ on the surface of the eyo, although effected spasmo<.licnlly and therefore with much greater force than can be done voluntarily, should be sufficient to cause by r flex action the secretion of tears in the many c es in which this occurs during violent expiratory efforts. Another cause 1nay come conjointly into play. 'Vo have seen that the internal parts of the eye, under certain conditions, act in a reflex manner on th lacrymal glands. We know that during violent expiratory fforts the pr ssure of the arterial blood within th vess Is of the ey is increased, and that the |