A demonstration of the effects of CO 2 upon the frog's pupil

Abstract

Frogs placed in an atmosphere of CO₂ gas show within thirty seconds, before any symptoms of excitement, a good constriction of the pupil. This constriction becomes almost maximal within five minutes; there is no dilatation.

The same effect is exerted by CO₂ gas upon excised frog's bulbi.

When the frog's iris, in the excised bulbus or in the living animal, is under the influence of CO₂ gas, the powerful mydriatic effect of adrenalin is strongly reduced.

Since CO₂ produces this myotic action upon excised bulbi, its effect must be exerted, largely at least, upon the sphincter pupillæ, that is, its action is peripheral. These experiments, however, do not exclude a possible central action.

This myotic effect of asphyxia in frogs is interesting, as asphyxia in mammals produces chiefly dilatation.