CHAP, vi.] SOME OTHER SENSATIONS. 1047 



produced their effects without giving rise to any sharp and 

 decided change of consciousness ; many of these are probably 

 afferent impulses of the common sensibility of which we are 

 now speaking. 



If we suppose that the skin in common with the other tissues 

 of the body possesses this common sensibility, and if we further 

 suppose that in the skin as elsewhere, these afferent impulses 

 when developed, as is the case under normal circumstances, to a 

 slight extent only are not distinctly recognized by consciousness, 

 and that when they do assume such a magnitude or intensity as 

 to break in upon consciousness the change of consciousness 

 which they produce is of the kind which we call pain, we reach 

 a conclusion which is also supported by other considerations. 

 On the one hand such a view is in accord with the conclusion 

 that cutaneous sensations of pain are wholly distinct from and 

 developed in a wholly different way from sensations of touch 

 and temperature ; and, as we shall see, to this conclusion we 

 are led by several different arguments. On the other hand it 

 relieves us from the following difficulty. It may happen to a 

 man to suffer pain in a particular region or tissue of the body, 

 once only in the course of his lifetime or possibly not even once ; 

 nay, we may suppose that in this or that region or tissue pain is 

 felt once only in one individual among a large number of per- 

 sons. If we suppose that pain is not as suggested above an 

 excessive phase of something which is continually going on in 

 a lower phase, but a something by itself quite distinct from all 

 other sensations, we are driven to conclude, since such a sensa- 

 tion must have a special mechanism, including special afferent 

 nerve fibres to carry it out, that in the case in question such a 

 mechanism of pain has been preserved intact but unused through 

 whole generations in order that it may once in a while come 

 into use ; which is in the highest degree improbable. This diffi- 

 culty disappears if we suppose that the constantly smouldering 

 embers of common sensibility may be at any moment fanned into 

 the flame of pain. 



We may conclude then that the skin in common with other 

 tissues possesses common sensibility, and that when this is ex- 

 cited in excess, so as to distinctly affect consciousness, we call 

 it pain. We thus experience through the skin three kinds of 

 sensations, those of touch, of temperature, and of common sensi- 

 bility, but the two former only are developed by further psychical 

 processes into perceptions ; it is by them alone that we obtain 

 through the skin knowledge of external objects. 



$ 1652. There is another consideration to be taken into view. 

 The agents which applied to the skin produce pain, act violently 

 on the skin, in many cases injuring the epidermis and affecting 

 the dermis. Moreover if the epidermis be removed, and the 

 stimulus, mechanical, thermal or chemical, be applied to the 



