Page:WHR Rivers - Studies in Neurology - Vol 1.djvu/36

22 said to be warm, and was one of the greatest difficulties against which we had to contend (vide p. 286).

A most disturbing condition, familiar to all who have investigated cases of lesions of the spinal cord, is the tendency of the patient to call all temperature stimuli, whether hot or cold, by the same name. It is important, under such circumstances, to interject frequent stimulations with a tube that is neither hot nor cold to the normal skin. Then it may be discovered that the neutral tube is as frequently said to be hot or cold as one which is a positive thermal stimulus to the normal hand.

Cerebral lesions do not as a rule abolish sensation to heat or to cold; ice and water at 45° C. are usually appreciated without difficulty. But such temperatures form a ready method of applying measurable affective stimuli, especially in cases of the so-called "thalamic syndrome." Extremes of heat and cold are uncomfortable or even painful, whilst warmth is usually distinctly pleasant. To study this affective aspect of sensation it is generally advisable to apply the stimulus to a larger area, and for this purpose we have used large copper tubes with a diameter of 4 cm. filled with water at various temperatures.

In cases of cortical injury or disease it is important to determine the power of distinguishing the relative warmth of two tubes, each of which is recognised as warm. One of the most interesting defects in such cases is the inability to appreciate with any certainty the difference between 35° C. and 45° C.; and yet both are said to be warm. Sometimes the loss of discrimination is less severe, but the patient cannot appreciate the difference between 33° C. and 40° C.

Occasionally it is important to determine the threshold for heat and for cold on similar portions of the two halves of the body; this gives the range of the neutral zone, which may be considerably enlarged as the result of a cortical lesion. This is frequently an extremely difficult and unsatisfactory form of examination, for most patients possess no word which expresses a neutral sensation. Before we begin testing with this purpose we therefore suggest that the answer shall be "warm touch," "cold touch," or "nothing but a touch." At the same time we compare the sensation evoked by the neutral temperature with that of a distinctly warm or cold tube.

During the experiments on my hand we were much occupied with the site and mode of reaction of the heat- and cold-spots. They are of purely scientific interest, and can rarely be tested under clinical conditions. The cold-spots were sought for with copper rods of about 1 mm. in diameter, which were placed in a glass containing broken ice; on removal, each rod was carefully wiped and, after its flat base had once been applied to the skin, was returned to the ice.

For the discovery of heat-spots we used a simple method which, as far as we can discover, has not been described before. We chose a "soldering iron" consisting of a large copper block fixed to an iron rod let into a wooden