IN A PREVIOUS article1on Scheerer's phenomenon, we stated how, in the course of our research and after many trials, we had succeeded in building a simpler and better apparatus for its observation. Scheerer's phenomenon is the entoptic perception of one's own blood cells circulating in the perimacular capillaries and the closest precapillary arterioles and postcapillary venules. We refer to the luminous points as blood cells, refraining from designating them as white or red, since this is still a moot question that has received contradictory answers from various authoritative sources. There is no doubt, however, that the phenomenon is connected intimately with the blood circulation. The instrument * consists fundamentally of a metal box containing a mercuryvapor grid and a diffusing screen. On the upper part of the box there are two openings through which the light is seen. In the oculars there are filters that permit the passage of