Franz, Sensations Following N erve Division. 223 



movements. The results, I believe, cannot be explained, as von 

 Frey has attempted to explain all of Head's results,'^ as a difference 

 in threshold values ; for in traction we deal with amounts of stimuli 

 much greater (or at least on normal parts they appear much greater) 

 than that of brushing the hairs with cotton wool. Such a two-fold 

 function in the hairs is in ac-cord with the findings of a two-fold 

 nerve supply to the hairs,* although the results on animals have 

 not been confirmed for the common (bodily) hairs of man. So 

 far as I am aware, the only results to be compared with these on 

 the hair sensibility are those on temperature sensations to be reported 

 in the next section and the few results by Head and Sherren 

 on temperature sensations. In one or two cases these authors, it will 

 be remembered, found parts of the skin not sensitive to hot (above 

 45° C.) and to cold (below 10° C.) objects, but found the same 

 parts when stimulated with temperatures of moderate degree to be 

 sensitive and to give appropriate warm and cool sensations. 



III. Temperature Sensations. 

 From examinations of normal individuals it appears that there 

 are special points on the skin that react to stimuli by giving a sensa- 

 tion of heat or cold, but that in the small areas between these 

 temperature points no sensations of hotness or coldness can be evoked 

 by stimuli. On the other hand, when we stimulate the skin with 

 areas of heated or cooled objects rather than with points the sensa- 

 tions of warmth or coolness result. The areal sensations appear to 

 differ from those in which separate spots are stimulated in that only 

 one sensation is obtained, and there is not an apparent mixture of 

 heat and cold from the spots that may be stimulated in the area. 

 For the understanding of these differences in sensation no explana- 

 tion has been offered that meets with imiversal approval, but the 

 analogy of the rods and cones in the retina has been made. It is 



'von Frey. The Distribution of Afferent Nerves in the Slvin. Jour. Arner. 

 Med. Assrt., 1906, vol. 47, pp. 645-648. 



'F. Tello. Terminaciones sensitivas en pelos y otros organos. Trah. del. 

 lah. de Invest. Biol, de la Univ. de Madrid (S. Ramon y Cajal), 1906, 

 tomo 4, pp. 49-77. 



