736 



SPECIAL SOMATIC AND VISCERAL RECEPTORS 



is pressed upon the skin with a force sufficient to elicit different in- 

 tensities of tactile impressions. This method permits of the deter- 

 mination of the acuity of these sen- 

 sations as well as of our ability to 

 localize them with accuracy. Esthes- 

 iometers are also in use which possess 

 two points of contact adjusted at 

 varying distances from one another. 

 This arrangement allows us to deter- 

 o> mine how far these points must be 

 separated from one another in order 

 .j to give rise to two distinct sensations. 

 Our ability to tell whether a tactile 

 stimulus is single or double, is known 

 as tactile discrimination. 

 "'* Tactile Acuity, Localization and 



Discrimination. We have seen that 

 tha adequate stimulus for sensations 

 of touch is a mechanical impact which 

 causes a deformity of the surface of 

 the skin and thus activates the sen- 

 sory nerve-endings contained therein. 

 This activation, however, is accom- 

 largement at end of core; c, nuclei of plished under normal condition with 



cells of core; t, nuclei of cells of outer th hd f H j adjuncts consist- 



tunica; t , inner tunica (Sobotta) X .. J 



380 diameters. ing m peculiar capsular investments 



of the terminals of the sensory nerve 



fiber. Thus, we find that the threshold value of a stimulus applied 

 to the tactile capsule, is very much lower than that required to 



FIG. 363. HERBST CORPUSCLES OF 



DUCK. 



n, Medullated nerve-fibrg; a, its 

 axis-cylinder, terminating in an en- 



FIG. 364. KHAUSE'S CORPUSCLE. A AND B, GENITAL CORPUSCLES FROM THE CLITORIS OF 

 THE RABBIT (Izquierdo) ; C, FROM THE HUMAN CLITORIS. (W. Krause.) 



elicit a sensation from the nerve fiber itself. It is evident, there- 

 fore, that the skin is in possession of what might be termed tactile 



