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 we used the method suggested by McDougall [22]. The compass-points were set at a certain distance from one another; they were then applied to the part to be tested in such a way that sometimes two points, sometimes one point only, touched the skin. The stimuli followed one another in an entirely irregular order, but so that, ultimately, H. had been touched ten times with one point, ten times with two points. Each correct answer was marked with a stroke, whereas a mistake was recorded by a cross. Thus if he answered "one," when touched with two points, a cross was placed below the line; if one point had been called "two," the cross was marked above. By this method it was at once obvious in how many instances he had answered correctly among the ten single and ten double stimuli. The answers whether right or wrong were ranged in strict sequence above and below the horizontal line.

Perfect appreciation of the compass-points at a distance of 4 cm. would be represented thus—

If, however, H. was unable to differentiate the two points, answering "one" to every stimulation, the record would stand—

Less complete failure would be represented by some such formula as—

In the following chapters these records are translated into the number of answers which were right (R.) or wrong (W.) for the sake of simplicity.

Observations made before the operation showed that the threshold for the flexor aspect of the left forearm lay at about 3·5 cm., when the compass-points were applied in the longitudinal axis of the limb. Over the radial half of the back of the hand, under similar conditions, it lay between 1·5 cm. and 2 cm.

Of all sensory tests, the results obtained with the compasses are most influenced by accessory conditions. A stranger entering the room, or anything that disturbed the quiet state of internal absorption, would at