This instrument enables one to localize accurately and quickly hyperesthetic segments of the body. A freely movable wheel (fig. 2) with sharp, closely set, radiating points is mounted at one end of the instrument. This wheel is lightly applied to the skin and then drawn across the area being investigated. The patient will feel pain as it crosses the hyperalgesic areas. When applied parallel to the spine. and about 2 inches (5 cm.) from the midline of the back, all the segments from the neck to the sacrum can be quickly tested. A rather constant pressure can easily be maintained along the course of the application.
At the other end of the instrument is a small disk wheel (fig. 3), freely movable, which has a rather sharp but not a cutting edge. This is used in a similar manner, excepting that greater pressure is exerted on it as it is drawn