THE SKIN AND COMMON SENSATION. 995 



through their end-organs but immediately along their course. He argued that 

 the pain felt when the ulnar nerve is cooled by holding the elbow long enough 

 in ice-cold water, is caused by excitation of the nerves of temperature sense. 

 But in that experiment, sensations tactual and thermal as well as dolorous, arise, 

 referred to the peripheral distribution of the ulnar trunk. The experiment 

 admits just as well of explanation by the hypothesis of special pain nerves 

 irritable in their course. 



It may be argued, however, that even on the view of the existence of 

 specific pain end-organs in the skin, it is not obligatory to suppose that, 

 though they respond equally both to tangible and thermal stimuli, they 

 are in reality of more than a single kind. These stimuli are of the 

 nature of general nerve excitants. They only excite the pain sensations 

 when they are applied in relatively high intensity, and excite it cceteris 

 paribus in proportion to the height of grade of their intensity. Such 

 excitants of sufficient intensity, when applied to any naked nerve fibre, 

 motor as well as sensory, and in its course, as well as at its ramified end- 

 ings, will excite it. What is necessary, therefore, in the skin is that the 

 endings of the hypothetical specific pain-nerves should be amenable both 

 to tangible and thermal stimuli, and this might possibly be the case in 

 one of two ways. They might possess end-organs so highly differentiated 

 in regard to specific nerve energy, that any stimulus affecting them at 

 all irritated pain-reaction. Or they migbt, while their central con- 

 nections obeyed to the letter the well-worn law of specific nerve 

 energies, be provided with peripheral end-organs so little differentiated 

 as to allow with facility a considerable range of quality of general 

 nerve excitants to play upon them with tolerable effect. The main 

 difficulty is that the effect is so great. Choice between the two views 

 will depend largely upon the relative value attached to two different 

 functions seeming to belong to every sensifacient end-organ. The 

 sensorial end-organ is an apparatus by which an afferent nerve fibre is 

 rendered distinctively amenable to some particular physical agent, and 

 at the same time rendered less amenable to, i.e. is shielded from, other 

 excitants. It lowers the value of the limen of one particular kind of 

 stimulus, it heightens the value of the limen of stimuli of other kinds. 



Especially in regard to the latter result of adaptation, has the original 

 Mullerian law of specific nerve energies required reconsideration. The Blix- 

 Goldscheider cold spots of the skin evoking cold sensations reply 1 to 

 stimuli of pressure and heat as well as of cold ; that is, non-adequate as well as 

 adequate stimuli fairly easily evoke from them their specific sensation. On 

 the other hand, there are in the tongue individual papillae from which only a 

 certain suitable set of tasteable substances can evoke a sensation, always the 

 specific sensation, and all other stimuli fail to evoke any sensation whatsoever. 2 

 The warmth spots of the skin are in the condition of these tongue papillae ; 

 but it may be that the pain spots are more in the condition of the 

 cutaneous cold spots in this respect, and even overpass them. Somewhat 

 against this is the histological evidence of the skin regions which are pre- 

 eminently dolorific, pre-eminently possessing so-called "naked" nerve fibril 

 sensorial endings. If simplicity of histological structure in a sensorial end- 

 organ be any guide to absence from it of functional differentiation, histology 

 indicates the explanation of the presumed amenity of pain spots to various 



1 Denied by M. Dessoir and Nagel, affirmed by Goldscheider, v. Frey, and Kiesow. 

 My own experience on this point supports the latter group of observers, and would include 

 faradisation. 



* Oehrwall, Skandin. Arch. f. PhysioL, Leipzig, 1891, Bd. ii. S. 1; cf. Kiesow, PhiL 

 Stud., Leipzig, 1898, Bd. xiv. S. 591. 



