was completely below the threshold; every double stimulation was said to be "one." He was allowed again to settle himself in the armchair and R. continued to test him with the points of the compasses at the same distance. With the return of the somnolent state the records improved; the total sixty stimulations gave the formula—
| 4 cm. | 1 | 21 R. | 9 W. |
|---|---|---|---|
| 2 | 26 R. | 4 W. |
but of these the first and second twenty obtained when H. was more nearly asleep were better than the last series.
| 4 cm. | 1 | 6 R. | 4 W. |
|---|---|---|---|
| 2 | 9 R. | 1 W. |
| 4 cm. | 1 | 7 R. | 3 W. |
|---|---|---|---|
| 2 | 10 R. |
This sleepy condition which is so favourable for results with compasses is one that requires absolute freedom from all external appeal to responsible action. It is a condition which H. has never succeeded in producing surrounded by the multifarious interruptions of home.
Conversely, concentration on the details of the compass-test greatly diminished the accuracy of H.'s answers. During a large number of examinations, directed towards elucidation of the phenomenon of "double ones," H. was asked to state whether the two sensations seemed to be far apart and, if possible, to indicate the position of the two spots. This required much concentration of attention on the details of testing and considerably raised the threshold.
To measure the power of appreciating roughness, we used Graham Brown's æsthesiometer. This instrument consists of a smooth metal surface from which small cylinders can be made to project for a measurable distance. In the pattern we used, a complete turn of the screw caused each of the six small cylinders to project 0·5 mm. As each complete turn was divided into ten equal parts, each of these divisions represented a projection of 0·05 mm.
The smooth surface was passed across the skin, and then the cylinders were made to project until a sense of roughness or "raking" was produced. In every case, the most careful comparative observations were made over similar parts of the sound limb.
For some of our observations on localization, we used the method of Victor Henri [19]. H. was given a life-sized photograph of the back of his hand and was told to mark on it the spot stimulated. But for the majority of our observations, we depended on verbal description of its position or on pointing with the index of the right hand. H.'s strong powers of visualization rapidly led to the development of what
