468 THE SENSORY FUNCTIONS OF THE SKIN 



sation of pressure accompanying the stimulus fails, while the painful after-effect 

 appears very vividly. 



With regard to the topographical distribution of the pain spots we learn 

 from v. Frey and others that on the back of the hand over the metacarpus 

 of the ring finger 16 pain points, as against 2 pressure points, can be demon- 

 strated within 12.5 sq. mm. i. e., 1.3 pain points to the square millimeter. 



From reasoning which we need not enter into here v. Frey has reached 

 the following conclusions with regard to the anatomical structures which may 

 possibly serve as the end organs of the different cutaneous nerves : 



(1) Among the well-known sensory nerve endings on parts devoid of hair 

 there is only one form which occurs in sufficient number to fulfill the require- 

 ments of an end organ of the pressure points, namely, the tactile corpuscles of 

 Meissner. According to this discoverer there are e. g., over the metacarpus 

 of the little finger in 1 sq. mm. one to two of these corpuscles which agrees well 

 with the number of pressure points in the same place. 



(2) These corpuscles however are quite exclusively confined to the parts 

 devoid of hair. Anatomical investigations have brought to light the presence 

 of a wreath of nerve fibers encircling the hair follicles down close under the 

 opening of the sebaceous glands, their terminal processes penetrating the walls 

 of the follicle as far as the glassy layer. This wreath of nerve fibers which 

 occurs with the greatest regularity in every hair follicle may be the end organ 

 of the pressure points associated with the hairs. 



(3) The sensation of pain is probably aroused by stimulation of some mech- 

 anism lying nearer the surface. Since only free intraepithelial nerve endings 

 are found external to the tactile corpuscles, we may look upon these as the organs 

 of the (superficial) sensations of pain in the skin. 



(4) Finally, v. Frey and Thunberg, the latter by careful analysis of the 

 different phenomena attending stimulation with heat, have made it probable that 

 the end organs of the heat nerves lie deeper than those of the cold nerves, also 

 that the latter lie deeper than the end organs of the pain nerves. 



EEFERENCES. M. G. Blix, Zeitschrift fur Biologic, Bd. xx, xxi, 1884, 1885. 

 M. v. Frey, Abhandl. d. mathem.-phys. Cl. der konigl. sachs. Ges. d. Wiss., Bd. 

 xxiii, No. 3, 1896. A. Goldscheider, Archiv fiir Anat. und Physiol., physiol. 

 Abt., 1885, suppl. Bd. A. Goldscheider, " TJeber den Schmerz," Berlin, 1884. 



