Page:Mind (New Series) Volume 6.djvu/462

 446 NOTES AND NEWS. ADEQUATE THERMAL STIMULATION. Working in this way, and using thermal stimulation, I have been able to once more corroborate Blix observations. Dessoir and Kiesow seem to have neglected the rules laid down above, simple and indispensable as they may appear. Hence their assertions. I may perhaps also mention the following facts. A hundred and twenty-six medical students have, during the last ten years at the Physiological Laboratory here, mapped out their temperature-spots on different parts of then- skin. When tested (eyes shut) they have hardly ever been found to make a mistake. The fact that surfaces of up to one square centimetre and more can be found, from which no thermal sensa- tions at all can be got, is perhaps the best proof that the whole of the skin is not sensitive to warmth and cold. The temperature-spots differ from each other as to their sensibility, so that some spots need a stronger stimulus to bring forth a just percep- tible sensation (minimum perceptibile) than others, but also so that some spots give a remarkably stronger sensation than others when stimulated by metal-points of the same temperature. These two factors seem to run parallel. MECHANICAL STIMULATION. Goldscheider was the first to observe that the temperature-spots can be excited by mechanical means for instance by a sharp-pointed bit of wood. Donaldson and Kiesow have found this true. In fact, some of my cold-spots seem so sensitive to this kind of stimulus that the lightest touch brings forth a sensation of cold. By mapping out on the skin with cold and warm points all temperature-spots within a certain space, and then, eyes shut, letting another person excite them by pressure, an objective proof can be obtained of the efficiency of mechanical stimulation just in the same way as of thermal, as shown above. ELECTRICAL STIMULATION. (1) Induced Current. Special care must be taken so as to avoid thermal and mechanical stimulation when wishing to get temperature-sensations only from the excitation to be had with an induction-current. 1 Great stress must also be laid on the necessity of having the current of proper strength it is best to begin with hardly perceptible currents. The curious pricking sensation which this sort of stimulation generally excites hi the skin will be found, if the current is not too strong, to give place to & pure sensation of warmth or cold on the temperature -spots. On certain other spots (" pressure-spots ") it will give place to a peculiar hammering sensation a series of light knocks (" Hammern " according to v. Frey), whilst on still other spots (probably the most sensitive " pain-spots ") a smarting feeling will predominate. The cold-spots seem to answer to weaker currents and also more rapidly than the warm- spots do. (2) Constant Current. The temperature-spots cannot, as far as I can find, be stimulated by the constant current as such, even if the stimu- lation be made as punctiform as possible. No sensations, in fact, are obtained until the current is made so strong that evident electrolytic processes appear in the skin. But then they do result, almost always accompanied by pain so sharp that their existence becomes sometimes 1 Platina wire of about 0'17 millimetre diameter and of ordinary tem- perature ( + 18 C.) seems to meet the demand on the sort of electrode required.