972 CUTANEOUS SENSATIONS. 



the call for repetition of the " activity " of the organ gradually springs up and 

 cumulatively increases. The endings of the afferent visceral nerve fibres are 

 in this phase excited with increasing urgency, by adequate stimuli, of the 

 quality of which Ave are ignorant, but these stimuli may be in many cases of 

 mechanical kind. Summation perhaps plays a greater part in rendering them 

 effective than in the case of the adequate stimuli of the organs of the special 

 senses. The sensations they evoke seem almost all of them imbued with 

 displeasurable " tone," and they can culminate in physical pain. 



An essential constituent of common sensation derives from the locomotor 

 apparatus of the body, e.g. muscles, joints, etc. But the contribution by this 

 factor is not so copious as might have been supposed. There is a large 

 diversion of its stream of ingoing impulses to channels feeding the production 

 of presentations of environmental agents. In fact, the sensations from muscles 

 which influence, by their contractions, the various sense organs, may almost 

 be said to be lost in contributing a further quality to the sensations of the 

 sense organs which the muscles in question influence ; for these they stan- 

 dardise their spatial quale. They, many of them, acquire thus in a secondary 

 manner some projection. But their justifiable inclusion in common sensation 

 is shown by nothing more clearly than by their relation to pain. Under 

 circumstances for the most part exceptional, they contribute " fatigue," " cramp," 

 " rheumatic " pains, etc., to common sensation. 



Cutaneous sensation occupies in some ways an intermediate place 

 between the forms of special sensation and of common sensation. 1 

 Cutaneous sensation has, according to its species, a variable degree 

 of projection, but never that degree attaching to special sensation. The 

 ether vibrations which, impinging on the retina, evoke perception of a 

 light shining at a distance, impinging on the cheek, evoke perception 

 of a warm spot of skin. Even most " touches " are perceived not so much 

 as pure signs of the environment, as of our conscious " self " reacting 

 to an agent. But the position of cutaneous sensations in regard to 

 common sensation will depend on to what extent the cutaneous sensa- 

 tions be regarded as separable into specific kinds. If the view taken 

 in the articles on " touch " and " cold " and " warmth " sensations be 

 accepted, then the specific " warmth " and " cold " senses are, especially 

 the former, further from the special and projicient senses than is the 

 pure " touch sense " ; the converse is their order of propinquity to 

 common sensation. On the view that all these three senses can each 

 produce physical pain, all three are clearly contributory to common 

 sensation. 



On this view the, as they have been called,' 2 "regular" stimuli provoke 

 sensations less related to common sensation than do irregular excessive stimuli 

 applied to the same cutaneous apparatus. The important point for the present 

 argument is, that on this view the limits of physical pain include certainly 

 several senses, a group of senses. Its most familiar ministers are perhaps 

 cutaneous nerves, but in respect to it other nerves, those of deep structures, 

 have to be placed beside them. Hence the classification of pains into " super- 

 ficial'' and "deep"; 3 and, on the above view, the existence of the latter class 

 is of itself a guarantee further that non-painful sensations arise from the deep- 

 lying structures of the body. 



1846, Bd. iii. S. 2). 



2 See A. Fick, " Physiol, des Menschen," Wien, 1882, S. 133. 



3 Xavier Bichat, "Sensation externes et internes," " Anatomie geneiale," Paris, 1802, 

 tome i. p. 165. 



