400 ORGANS OF THE SENSES. 



We have already seen that Brown-Sequard (p. 46), allows 

 that these isolated conductors are found in the spinal axis, 

 and that he estimates their number as four, belonging to tem- 

 perature, pain, touch, and tickling (mention is made of the 

 muscular sense, which is entirely distinct from these, its con- 

 ductors being found in other strands of the axis). 



The difference in sensations may, however, be simply owing 

 to the specific energy of the terminal nerve organs, some of 

 which (corpuscles of Pacini) govern the sensations of pres- 

 sure, and others (tactile corpuscles), those of touch, or what 

 is called the sensation for localization in the skin ; while 

 others (still more difficult to define) regulate the sensations 

 of temperature and pain. If this be the case, a special ex- 

 citant will produce the corresponding special sensation only 

 when applied to these nerve terminations, and not when it 

 reaches the trunk of the nerve, the fibres of which form simi- 

 lar conductors. Thus if the elbow is dipped into cold water, 

 the ulnar nerve, excited by this change of temperature, will 

 occasion sensations extending to the inner side of the 

 hand (see p. 56) ; the sensation experienced in this case, in 

 the little finger, consists of a vague and undefined feeling of 

 pain, not of cold, which would be the case if the hand were 

 dipped in cold water. 



According to some authors, these sensations are only higher 

 or lower degrees of an excitation the nature of which is 

 always the same; looked at in this light, pain is only the 

 highest degree of excitation of the skin, whether by pressure 

 or by change of temperature ; while any excitation, of what- 

 ever nature, will excite the same sensation in a lower degree ; 

 thus, if a part of the skin be covered with a card, in which a 

 very small hole is made, and an excitant of any kind brought 

 to bear upon that portion of the skin which is exposed 

 through this hole, there will be no difference between the 

 sensations produced, whether they be caused by the applica- 

 tion of a red-hot coal, the prick of a pin, or by tickling with 

 a feather, etc. In spite of this experiment, however (experi- 

 ment byFick), 1 we can hardly admit that all these sensations 

 are of the same kind, and differ only in degree, when we see 

 that in certain pathological cases they may be independently 

 paralyzed, or that special subjective sensations may be pro- 

 duced. It is especially difficult to admit that pain is only 



1 See H. Taine, " De 1 'Intelligence." Paris, 1870, Vol. II. Book 

 III. Sensations du Toucher. 



