13 



RECENT ADVANCES 



IN THE 



PHYSIOLOGY OF THE SENSES, 



OF THE SENSES GENERALLY.* 



Influence of cold and heat on the nerves of sense. It appears, from some 

 ingenious experiments by Professor E. H. Weber, f that the prolonged 

 application of either heat or cold to nerves of ordinary or special sensation 

 diminishes, or suspends for a time, their power of conveying to the sen- 

 sorium the effects of impressions made on them. Professor Weber 

 found, for example, that on keeping the tongue immersed for from half a 

 minute to a minute in water heated to about 125 Fahr., and then bringing 

 it in contact with sugar, in powder or in solution, the sweet taste of the 

 sugar was no longer perceived. Moreover, the sense of touch, usually so 

 delicate at the tip of the tongue, was also rendered imperfect. A sensation 

 of numbness was induced in the organ, not unlike that perceived in a limb 

 when " asleep ;" and this sometimes remained for about six seconds, or 

 longer. A similar imperfection of taste and touch was produced by im- 

 mersing the tongue for the same length of time in a mixture of water and 

 broken ice. The cold as well as the hot fluid gave rise to a peculiar 

 sensation of pain in the immersed part: and so similar was the pain pro- 

 duced in each case, that from the sensation alone it was impossible to 

 ascertain whether the fluid used in the experiment was hot or cold. Weber 

 found also that when similar experiments were performed on the lips, the 

 fingers, and other parts, their sense of touch was impaired in the same man- 

 ner with regard to the perception of heat and cold : for, when two or more 

 fingers were held immersed for a minute or so in water heated to 125 

 Fahr., or cooled to 32 Fahr., they were found to have lost, for a time, the 

 power of discriminating between a hot and a cold fluid, or solid, body. As 

 in the case of the tongue, so also here, a sense of pain was produced in the 

 fingers during the immersion : this pain, which was the same whether the 

 fluid was hot or cold, is probably to be referred to the trunk, not to the 

 extremities, of the nerve of the immersed part. 



He found also that it was not necessary, in order to the diminution or 

 suspension of the sensitive powers of a nerve, that its extremities should 



* Book the Fifth, p. 1059 of Muller's Physiology. t Miiller's Archiv. 1847, p. 342. 



