Visual phenomena connected with the yellow spot

1. Loewi's experiment. If we look at a clear white suirface through a solution of chloride of chromium, which is of a celadon green colour, we shall see a purple spot in the centre which varies in size and shape with different persons. On careful examination it will be found to consist of three portions, the centre corresponding to the fovea appears as a bright purple disk, the middle corresponding to the non-vascular portion of the yellow spot appearing as a dark green ring, and lastly Loewi's ring corresponding more or less accurately to the outer feeble yellow portions of the yellow spot which appears as a purple ring surrounding the central portion and possessing a diameter twice or three times as large. 2. Apparent size of regions of yellow spot in field of vision. The region corresponding to the yellow spot occupies a considerable area in the field of vision. I find that the visual angle which any portion subtends can be easily measuired by projecting the after-image of an object occupying a known visual angle on the sky above a house. A comparison is easily made in both cases with portions of the house. If an observer look straight at the cloudless sky, preferably about three hours before the sun sets, for about ten to twenty seconds, a disk or an ellipse with the long diameter horizontal and which is to me of about nine degrees appears in the sky. Inside this is a central darker portion of about two degrees in each diameter and this surrounds a central