5. Tickling and Scraping.
Our investigations led us to seek stimuli which are largely affective, or which contain a considerable affective component. Apart from pain, it is difficult to obtain a stimulus of this kind, but tickling unquestionably evokes a sensation which is strongly affective and may be either pleasant or unpleasant. The easiest method to produce tickling is to draw the pulps of the fingers gently over the soles of the feet; in some cases this stimulus also tickles the palms of the hands. In certain persons a wisp of cotton wool rubbed gently over hair-clad parts produces tickUng, especially over the pinna, on the neck and on the hair behind the ears, although in many such a stimulus is entirely ineffective for this purpose.
Scraping with the finger-nails is also a definite affective stimulus of the unpleasant order, as may be seen in cases in which there is an exaggerated response to affective stimuli. In such "thalamic" patients it may produce an intensely unpleasant sensation.
6. Vibration.
To test the power of recognising vibration we have employed a large tuning-fork beating 128 vibrations per second (C).
The fork, vibrating strongly, is placed on some part of the body which is firmly supported on the bed or on a pillow. If it is normal, the patient at once recognises the "buzzing" sensation. His eyes are closed and he is asked to say when the vibration ceases; as soon as he indicates that it is no longer perceived, the fork is transferred to the corresponding portion of the other hand. Under normal conditions the vibration usually becomes appreciable again for a time. The period between the transference of the fork to the other hand and the moment when its beating can no longer be recognised, is measured with a stop-watch. In healthy individuals this may last from five up to fifteen seconds; but a few persons allow the fork to run down so far on its first application that it has ceased to beat before it is transferred. Both these modes of reaction are normal, provided the measured periods are approximately equal from right to left and from left to right. Thus it may happen that, in one form of normal response, the records read as follows for four observations:—
| Right to left. | + 6 sec. | + 4 sec. | ||
| Left to right. | + 5 sec. | + 4 sec. |
or, according to the other mode of reaction:—
| Right to left. | + 0 sec. | + 0 sec. | ||
| Left to right. | + 0 sec. | + 0 sec. |
In neither instance was there any material difference between the two hands.
