APPRECIATION OF TEMPERATURE. 657 



. By comparing the distribution of the tactile corpuscles with the results 

 given in the table, it will be seen that the sense of touch is most acute in 

 those situations in which the corpuscles are most abundant. In the space of 

 a little more than ^ of an inch (2'2 mm.) square, on the palmar surface of 

 the third phalanx of the index-finger, Meissner counted the greatest num- 

 ber of corpuscles ; viz., one hundred and eight. In this situation the tactile 

 sensibility is more acute than in any other part of the skin, the mean dis- 

 tance indicated by the aesthesiometer being 0*603 of a line, or 1*27 mm. 

 (Valentin). In the same space on the second phalanx, forty corpuscles were 

 counted, the aesthesiometer marking 1-558 line, or 3*27 mm. (Valentin), this 

 part ranking next in tactile sensibility after the red surface of the lips. 

 One can readily understand how the tactile corpuscles, embedded in the 

 amorphous substance of the cutaneous papillae, might increase the delicacy of 

 appreciation of slight impressions, by presenting hard surfaces against 

 which the nerve-filaments can be pressed. 



As regards those portions of the general cutaneous surface in which no 

 tactile corpuscles have been demonstrated, it is not easy to connect the varia- 

 tions in the tactile sensibility with the nervous distribution, as little is 

 known of the comparative richness of the terminal nervous filaments in 

 these situations. 



Appreciation of Temperature. It is not known that the sense of tem- 

 perature, either of the surrounding medium or of bodies applied to different 

 parts of the skin, is appreciated through any nerves other than those of gen- 

 eral sensibility or that there is any special arrangement of the terminations 

 of certain of the nerves connected with this sense. As regards the general 

 temperature, the sense is relative and is much modified by habit. This state- 

 ment needs no explanation. As is well known, what is cold for an inhabitant 

 of the torrid zone would be warm for one accustomed to an excessively cold 

 climate. Habitual exposure also modifies the sense of temperature. Many 

 persons not in the habit of dressing warmly suffer but little in extremely cold 

 weather. Those who habitually expose the hands or even the feet to cold, 

 render these parts comparatively insensible to temperature ; and the same is 

 true of those who often expose the hands, face or other parts to heat. The 

 variations in the sensibility of different parts of the surface to temperature 

 depend, also, upon special properties of the parts themselves. The differ- 

 ences, however, are not so marked as to be of any great importance, and the 

 experiments made upon this point are simply curious. 



The experiments of Weber and others show that the skin is the chief 

 organ for the appreciation of temperature, if the mouth, palate, vagina and 

 rectum, by which the differences between warm and cold substances is 

 readily distinguished, be excepted. In several instances in which larger por- 

 tions of the skin were destroyed by burns and other injuries, experiments 

 have been made by applying spatulas of different temperatures. In one of 

 these, a spatula plunged in water at 48 to 55 Fahr. (9 to 12 C.) was 

 applied to a denuded surface, and again, a spatula at 113 to 122 Fahr. (45 

 to 50 C.). When the patient was requested to tell which was the warmer. 



