28 PHYSIOLOGY CHAP. 



latter lie in the. deepest layer of the skin agrees well with 

 v. Frey's statement that the heat spots are the most difficult to 

 determine and have a longer reaction time. On the other hand, 

 it appears probable from an interesting observation by v. Frey 

 that the sensation of cold is dependent on the end-bulbs described 

 by Golgi and Mazzoni. The conjunctiva of the eye is insensitive 

 to pressure and heat, while its sensitiveness to cold, on the con- 

 trary, is very definite : Dogiel's observations show that the end- 

 bulbs are abundant in the conjunctiva. 



VI. Although the sensations of heat and of cold represent 

 two modalities which depend on distinct sense-organs they may 

 conveniently be discussed together, as most of the observations 

 on this subject gain in interest by comparison. 



Sensibility to cold and heat not merely includes the external 

 cutaneous surface, but also extends to the skin of the auditory 

 canal, and the mucous membrane of the nose, mouth, pharynx, 

 and anus. The conjunctiva of the eye and external mucous 

 membrane of the genital organs are insensitive to heat, but 

 sensitive to cold. The rest of the mucous membrane, e.g. in 

 stomach, intestine, etc., is totally destitute of any thermal sensi- 

 bility as E. H. Weber showed in 1851. 



We saw that it is easy by means of punctiform stimulation to 

 demonstrate that the two thermal senses are unequally distributed 

 in the different cutaneous regions, and that cold spots are much 

 more numerous than heat spots. 



Goldscheider, in order approximately to map out the distribu- 

 tion of thermal sensibility, experimented on different cutaneous 

 regions with thermo-aesthesiometers in the form of metal cylinders, 

 3-4 mm. in diameter. With this method it is possible to excite 

 a greater or less number of thermal points by heat and cold. If 

 the skin-surface investigated contains no thermal point, it has no 

 thermal sensibility, and its thermal sensibility varies according 

 as it contains many or few thermal points for heat or cold. It 

 must be noted, however, that the degree of sensibility is not 

 proportional to the number of excited sensory points, because the 

 excitability of the latter has been experimentally proved to vary 

 considerably : the presence of a few highly excitable points may 

 make one area of the skin appear more sensitive than another 

 which contains more thermal points that are less excitable. 

 Goldscheider's method does not therefore determine the greater 

 or less abundance of thermal points in different parts of the skin, 

 but merely the mode in which these react to ordinary stimulation 

 by heat and cold. 



Figs. 19 and 20 from Goldscheider's memoir illustrate the 

 results obtained by this method. They show that the sensibility 

 to heat is invariably less developed both in intensity and in 

 extent than that to cold. According to Goldscheider there is no 



