This article is only available in the PDF format. Download the PDF to view the article, as well as its associated figures and tables. The phenomenon of after-image has long been known and studied, but it has apparently not been utilized as a means of perimetry. It is reasonable to suppose that if an after-image were produced in a patient with a lesion of the central optic pathways, there might be a defect in the after-image corresponding to the site and size of the area of damage of the visual system. This hypothesis was tested according to the following technic. METHOD Technic. —The instrument used consists of a portable flood lamp with a 500 watt bulb and a 16 inch (40 cm.) reflector. Over the reflector is placed a translucent cover 0.5 mm. in thickness, made of two layers of white broadcloth, on the surface of which a standard visual field design is sewed in black, the lines being 5 mm. in width. The test is best carried out in a dark room with