Page:Brain Volume 31 Part 3.pdf/28

 over the long tendons sensibility seems to be less than over the parts between. After the operation, we avoided these situations as much as possible, especially when employing the finer thermal tests.

Many difficulties surround the testing of sensibility to heat and cold, particularly when dealing with intermediate degrees. A glass tube cannot be employed for finer observations, owing to the great difference between the temperature of its external and internal surfaces. We have, therefore, throughout used flat-bottomed silver tubes with a diameter of 1·25 cm. These tubes were filled with broken ice, or with water at the temperature desired, and contained a thermometer. They were never warmed or cooled from without. When used for testing sensibility to heat, several tubes ranged in a wooden stand were filled with water at temperatures considerably higher than those we wished to use for testing; from these, a tube was selected as soon as it had sunk to the temperature required. These silver tubes lose their heat so rapidly that it is possible to use the same one for a short series of tests only.

With such precautions, few difficulties attend the testing of sensibility to the more extreme degrees of heat and cold. But occasionally, when the part is sensitive to painful stimuli but insensitive to heat, a tube at 50° C. and above may be said to be hot, solely on account of the peculiar pain produced. H. soon learnt to differentiate this pain, due to a hot object, from a true sensation of heat; he frequently said, "Any ordinary patient would have called such stimuli hot, because the pain produced is of a kind associated in daily life with the action of hot bodies only. Further, a patient is told to say if he feels heat, cold, or a touch. Given, then, that he knows his thermal sensibility is being tested, he would certainly call the sensation I experience 'hot.

Occasionally, contact with a neutral tube would cause an indeterminate and somewhat tingling sensation over the affected area; this was frequently said to be warm, and was one of the greatest difficulties against which we had to contend.

Fewer difficulties surround the testing of sensibility to cold; but it must be remembered that a silver tube always seems colder than one of glass containing water at the same temperature, on account of the greater rapidity with which it abstracts heat. Cold stimuli, more particularly those used for testing cold-spots, are liable to cause a vaso-constriction, shown by a blanching of the skin. This condition is peculiarly unfavourable for all sensory tests.

The cold-spots were sought for with fine copper rods of about 1 mm.