SKIN-SENSATIONS 429 



spots, in others heat-spots, are more closely grouped. The 

 tongue and the hand, and especially the tips of the fingers, are 

 most sensitive to touch ; but whereas the tongue is also ex- 

 ceedingly sensitive to warmth, the hands are relatively insensi- 

 tive. Yet, speaking generally, parts especially sensitive to 

 touch are little sensitive to temperature, and vice versa. Sensi- 

 tiveness to cold is much more widespread than sensitiveness to 

 heat. It is concentrated in the skin covering the abdominal 

 viscera. A cold douche directed between the shoulders is 

 doubtfully felt as cold. There is no doubt whatever about it 

 when it strikes the skin over the stomach. 



From these observations it appears that the skin contains 

 three sets of organs sensitive respectively to touch, cold, and 

 heat. Certain investigators hold that it also contains specific 

 organs, or nerve-endings, sensitive to painful stimulants ; but 

 in this case there is the obvious difficulty of distinguishing 

 between pain and touch. At no spot can pure pain be evoked 

 free from any consciousness of touch. 



To a certain extent the combinations of epithelial cells and 

 nerve-endings in the skin fulfil the negative requirement of 

 sense-organs ; each kind, whilst specially sensitive to its own 

 specific stimulant, is insensitive to stimulants of other kinds. 

 But mutual exclusion is not absolute in the case of cold 

 and warmth. If a warmed metal point be applied to a 

 cold spot, it produces a sensation of cold. Our feelings of 

 warmth and cold are to a large degree comparative. Luke- 

 warm water feels cold to hands just taken out of hot water ; 

 moderately cold water appears luke-warm to hands that have 

 been in contact with ice. The sensory apparatus for cold and 

 heat soon adapts itself, or, in physiological language, it is soon 

 fatigued. If after a prolonged bath at the body temperature 

 a foot be plunged into very hot water and withdrawn quickly, 

 the feeling which first ensues is one of cold. It is indistinguish- 

 able from the feeling provoked by dipping the foot into cold 

 water. The sensation of cold subsequently gives place to one 

 of painful warmth. This does not indicate that the heat-spots 

 have been waked out of their lethargy by excessive stimula- 

 tion. On the contrary, it is the cold-spots which, when they 

 were first stimulated by the very hot water, answered " Cold," 

 that now cry out " Hot "; for both cold-spots and heat-spots, 



