484 STUDIES IN ADVANCED PHYSIOLOGY. 



a single nerve going to it, and so carries but a single im- 

 pulse, no matter in what part of the circle it is stimulated. 

 That this notion is wrong is clearly proved by the fact that 

 by practice this circle may be made much smaller, a thing 

 which would be utterly impossible if they were anatomical 

 units. The possible explanation is that the nerves coming 

 from certain portions of the skin run in such a way through 

 the centers in the cord or brain as to produce more of a 

 radiation into the neighboring fibers or cells, and so prevent 

 a very accurate localization. Practice in such a case would 

 be merely the experience to eliminate these radiations and 

 to be able to define the sensation at last to the exact nerve 

 fibers in question. 



It is given by some observers that on an average each 

 touch area contains about twelve touch corpuscles. If this 

 be really true, the explanation of these touch areas may 

 consist in the possible fact that the stimulation at any point 

 stimulates not only the touch corpuscle immediately under- 

 neath or next to it, but about a dozen of the adjoining ones, 

 and so a rather compound sensation is carried. Where 

 these twelve are closely huddled, as in the case of the 

 tongue or lip, the power to localize the affected spot would 

 be quite definite, while in the case of the scattered corpus- 

 cles at other portions of the skin, the area would be too 

 large for exact definition. 



THE SENSE OF TEMPERATURE. 



Not only is the skin able to perceive tactile impressions 

 but it is also able to take note within certain limits of the 

 temperature of the objects affecting it. This ability to per- 

 ceive the warmth of anything is, however, not an absolute 

 one like that of a good thermometer, but is only relative. We 

 are only able to tell whether a thing is hotter or colder than 

 the part of the skin affected, or when the comparison is en- 

 tirely between outside objects we are enabled simply to de- 

 termine of these which is the warmer. This may be easily 

 proved by immersing one hand in warm water and the other 



