Chap, vi.] SOME OTHER SENSATIONS. 1053 



special sense. We have no satisfactory experimental or other 

 evidence that stimulation of the olfactory fibres otherwise than 

 through the terminal organs will give rise to olfactory sensations. 

 We have evidence that stimulation of the centres by various 

 means will give rise to the specific sensations, but not that stim- 

 ulation of the fibres of the nerves themselves will. The branches 

 of the glossopharyngeal and fifth nerves distributed to the organs 

 of taste are, unlike the above, mixed nerves, and when they are 

 stimulated sensations other than specific taste sensations are also 

 developed, and the former might obscure the latter; still the 

 evidence so far as it goes supports the view that stimulation of 

 gustatory fibres otherwise than through their terminal organs 

 does not lead to the development of gustatory sensations. In 

 the case of touch the evidence is perhaps still stronger. We 

 must in any case suppose that each cutaneous nerve distributed 

 to a given area of skin contains fibres which subserve the sense 

 of touch exercised by that area, and which pass from the terminal 

 organs in that area, whatever their nature, to the parts of the 

 central nervous system, whatever they may be (§ 505), which act 

 as centres of touch sensations. If these fibres when directly stim- 

 ulated, apart from their terminal organs, necessarily give rise to 

 touch sensations, stimulation of the nerve itself while running in 

 the subcutaneous tissue should give rise to touch sensations. But 

 experience shews, as we said a little while ago, that this is not the 

 case. Whenever the nerve fibres themselves are directly stimu- 

 lated, as for instance when the epidermis is removed from the 

 skin or when a nerve is laid bare, then however they be stimu- 

 lated, be the stimulus weak or strong, if consciousness be affected 

 at all, the affection takes on the form of pain ; psychological 

 examination of the subjective result discloses nothing that can 

 be called a sensation of touch. A familiar instance of the dif- 

 ference between the effects of stimulating a nerve trunk, and 

 those of stimulating the cutaneous terminal organs of special 

 sense, is seen in the effect of dipping the elbow into a freezing 

 mixture. The cold affects the skin of the elbow and gives rise to 

 sensations of cold in that part ; but the cold, if intense enough, 

 also affects the underlying trunk of the ulnar nerve, and by 

 direct stimulation of the fibres in the trunk developes sensory 

 impulses ; these impulses however are those not of sensations of 

 cold, but of pain ; and the pain, in accordance with a principle 

 to which we shall presently call attention, is referred to the ter- 

 minal distribution of the ulnar nerve on the ulnar side of the hand 

 and arm. In speaking above (§ 651) of pain we said that exces- 

 sive pressure or excessive heat or excessive cold applied to the 

 skin, overrides or annuls pressure and temperature sensations 

 and gives rise to mere sensations of pain ; and it might be urged 

 that when a nerve is directly stimulated the specific sensations 

 of touch and temperature are similarly annulled. But in the 



