22 SPECIAL SENSES. 



Titillation. The sensation experienced when certain parts 

 of the general surface are subjected to titillation cannot easily 

 be described, though it is sufficiently familiar. This sensa- 

 tion is simply due to delicate impressions made in unusual 

 situations, and is remarkable chiefly on account of the reiiex 

 movements which it occasions. If the soles of the feet be 

 tickled, it is almost impossible to avoid movements of the 

 limbs. These are not due entirely to the peculiar sensation 

 appreciated by the brain, for the same stimulus, in persons 

 suffering from complete paralysis of sensation and voluntary 

 motion of the lower extremities, may produce even violent 

 action of the paralyzed muscles. These phenomena have been 

 fully described in connection with reflex action. There are 

 no facts, experimental or clinical, showing that the peculiar 

 sense of titillation is conveyed to the encephalon by nerve- 

 fibres other than those of general sensibility. The peculiar 

 nature of the sensation is due to the unusual character of the 

 impression, and does not involve the action of special nerve- 

 fibres as conductors. 



Appreciation of Temperature. It is not known that the 

 sense of temperature, either of the surrounding medium or of 

 bodies applied to different parts of the skin, is appreciated 

 through any other nerves than those of general sensibility, 

 or that there is any special arrangement of the terminations 

 of certain of the nerves connected with this sense. As re- 

 gards the general temperature, the sense is relative, and is 

 much modified by habit. This statement needs no explana- 

 tion. As is well known, what is cold for an inhabitant of the 

 torrid zone would be warm for one accustomed to an exces- 

 sively cold climate. 1 Habitual exposure also modifies the 

 sense of temperature. Many persons not in the habit of dress- 

 ing warmly suffer but little in extremely cold weather. Those 



1 We do not take into account, in this connection, the remarkable fact, that 

 inhabitants of warm climates, for a certain time, may bear long-continued ex- 

 posure to cold better than those accustomed to a lower temperature. 



