SENSE-ORGANS 347 



cold. We cannot be certain of the detail, small 

 differences of temperature cannot be recognised, a prick 

 is felt but the place where the prick was given is not 

 known with certainty. We must not press the analogy 

 of the microscope too far however. We might by 

 accident obtain a clear vision of the slide without recourse 

 to the fine adjustment of the microscope. No accident 

 would produce for us detailed sensations without the 

 corresponding mechanism in our skin. 



For the trustworthy information which we possess on 

 this subject we are indebted to the devotion of a 

 physician who allowed the sensory nerve from part of the 

 skin of his arm to be cut. The nerve grew again, and as 

 the various sensations returned at different times, it was 

 possible to distinguish between them. After about three 

 months the rough as opposed to the detailed sensations 

 come back, a rough appreciation of temperature and a 

 rough sensation of pain -a thing which was really hot 

 could be felt to be hot, a thing which was really cold 

 could be felt to be cold, but he found it impossible to tell 

 which was tlie hotter of two bodies which were nearly of 

 the same temperature. To these rough sensations the 

 name protopathic was given. The mechanism by 

 which they are felt is that to which we have compared the 

 coarse adjustment of the microscope. For a long time 

 the skin had these sensations and these only. Then at a 

 much later date, the delicate sensations returned— those 

 of detailed touch, the ability to distinguish the contact 

 of a single point from that of two points in close prox- 

 imity, the power of appreciating small differences of 

 temperature and the exact localisation of trifling pains, 

 these sensations were called epicritic. The sensory 

 end organs of these— both protopathic and epicritic -are 

 situated in the skin. 



Protopathic sensations, specially those of pain, are 

 not contined to the skin but spread over a much greater 



