SENSE OF TOUCH. 731 



pathological observations of M. Brown-Sequard 1 strongly support the view 

 that such separate conductors do exist, and he even believes he has demon- 

 strated that the nerves conducting these four kinds of impression from the 

 inferior extremities and greater part of the trunk after decussation are situ- 

 ated in the upper part of the Spinal Cord, behind the corresponding group be- 

 longing to the upper limbs and the neck ; and Horvath 2 has made the curious 

 observation, that if the fingers be kept for some time in alcohol, only a few 

 degrees (8) above the freezing-point, whilst the tactile sensibility is retained, 

 the prick of a needle is not felt. The experiments made by Weber 3 to de- 

 termine whether there are special conductors for temperature, in which he 

 applied spatulas of different temperature (48 arid 122 F.), to the surface 

 of the skin denuded of its integument by a burn, and found that only pain 

 was experienced, are of little value. It is remarkable, however, that we 

 cannot excite impressions of heat or cold by direct application to the trunks 

 of nerves which we know must conduct such impressions; for the parts of 

 the skin, immediately beneath which lie large nerve-trunks, are not more 

 sensitive to moderate heat and cold than are any others ; whilst a greater 

 degree of either is felt as pain, not as a change of temperature. Thus, a 

 mixture of ice and water applied over the uluar nerve, affects it in fifteen 

 seconds, and produces severe pain, having no resemblance to cold, and such 

 as cannot be excited by the same degree of cold applied to any other region. 

 So the nerve of the tooth-pulp is equally and similarly affected by water of 

 43 and of 112 ; either application causing a pain exactly similar to that 

 excited by the other, or to that produced by pressure. The same is true of 

 the impressions received through the skin itself, when they pass beyond cer- 

 tain limits of intensity ; thus, the sensation produced by touching frozen mer- 

 cury is said to be not distinguishable from that which results from touching 

 a red-hot iron. Wislicenus 4 and Fick, moreover, found that sensations of 

 heat, even in the most sensitive parts of the body, were sometimes mistaken 

 for those of contact. Thus in the case of the hand, an erroneous conclusion 

 was arrived at six times out of 105 trials, and on the back twelve times in 

 30 experiments. The perception of variations of temperature does not ex- 

 tend in the mucous membranes far beyond their external orifices. Thus, 

 Weber found that on drinking a tumbler of water 32, he felt the cold water 

 in the mouth and pharynx, but its passage into the stomach could not be 

 perceived. There was, it is true, a slight sensation of cold in the gastric re- 

 gion, but as it only occupied the situation of the anterior wall of the stomach., 

 it was attributable to the abstraction of heat from the abdominal integu- 

 ments in contact with this. On drinking three glasses of milk at 158, 145, 

 and 140, the sensation of heat could not be traced lower down than that of 

 the cold in the previous experiment. In like manner, the injection of four- 

 teen ounces of water at 65 into the rectum produced scarcely any sensation 

 of cold, though on its return, a few minutes afterwards, a distinct feeling of 

 cold at the anus. When water at so low a temperature as 45.5 F. was in- 

 jected, the first feeling excited was a sensation of cold in the immediate 

 neighborhood of the anus, and then a feeble movement in the bowels ; but, 

 a little time afterwards, there was a faint sensation of cold, especially in the 

 anterior wall of the abdomen. This sensation, however, remained after the 

 return of the water ; and may hence be attributed to the abstraction of 

 warmth from the abdominal integuments, which was proved to have taken 



1 Archives de Physiologic, 1868, vol. i, p. 610; see also Sieveking, Med.-Chir. 

 Rev., 1858, p. 280; Spring, Presse Medicale, 1864, No. xxxiv. 



2 Centralblatt, 1873, p. 208. 3 Muller's Archiv, 1849, p. 273. 

 4 Henle and Meissner's Bericht, 1859, p. 632. 



