Comparative studies on the physiology of the iris. -I. Selachians

Abstract

The iris of fish first attracted attention on account of the fact that its sphincter muscle contracts under the influence of light, even after the eye has been removed from the head. This phenomenon has been studied by Steinach, Magnus, Guth (1901), Franz (1905 and 1906), and recently by Herk (1928 and 1929). These researches have shown that in Cyclostomes, Selachians and many Teleosts the incidence of light gives a stimulus directly to the sphincter muscle (without the mediation of any nervous mechanism), causing it to contract. It has recently been showm, however (Young, 1931), that in one Teleost at least, Uranoscopus , there is a nervous mechanism and that the direct effect of light on the iris plays no important part in its normal movements. This mechanism itself is of considerable interest in that it is the reverse of that found in Mammals, and it seemed worth while to make a closer examination of the iris of other to discover whether a nervous mechanism is present in any other cases. The pharmacology of the iris has never been thoroughly studied. Steinach, Beer (1894) and Guth (1901) showed conclusively that atropine, even in concentrations of 2 percent., did not, a least for a considerable time, inhibit the narrowing caused by illumination of the pupil of an isolated eye. Young (1931) Showed that pilocarpine, eserine, acetyl choline, and adrenaline all constrict the pupil of Uranoscopus , but the methods used were rough.