The sensitiveness of the eye to impressions is increased by strychnine, the field of vision becoming larger, and the sight more acute, so that objects can be distinctly observed at a greater distance, and the field of colour is increased for blue. This action appears to be to a certain extent local, as it occurs more distinctly on that side where the strychnine has been injected hypodermically. The sense of colour is affected in a remarkable way by santonin, which at first causes objects to appear somewhat violet and afterwards of a greenish-yellow. The yellow colour has been ascribed to staining of the media of the eye by santonin, as it becomes yellow when exposed to the light; others again have supposed the alteration in the apparent colour of objects to be due, first to a stimulation, and then to a paralysis of those constituents of the retina by which the violet colour is perceived.

1 Engelmann (and von Genderen Stort), Pfuger's Archiv, xxxv. p. 498.

2 Gradenigo, jun., Allg. Wiener med. Ztg., 1885, No. 29.

The sensibility of the eye for red and green appears to be sometimes diminished by physostigmine.