PARTS OF ANIMALS, III. x. 



what actually happens : whenever, o\ving to their 

 proximity, they draw up the hot residual fluid, this 

 at once causes a recognizable disturbance of the 

 intelligence and of sensation. And that is why they 

 are called phrenes : as if they took a part in the act 

 of thinking (pkronein). This of course they do not 

 do ; but their proximity to those organs which do 

 so take part makes the change of condition in the 

 intelligence recognizable. That, too, is why the 

 phrenes are thin in the middle ; this is not due 

 entirely to necessity (though as they are fleshy to 

 begin with, the parts of them nearest the ribs must 

 of necessity be more fleshy still) ; there is another 

 reason, which is, to enable them to have as little 

 moisture in them as possible, since if they had been 

 wholly of flesh they would have tended to draw 

 to themselves and to retain a large quantity of 

 moisture. Another indication that it is when heated 

 that they quickly make the sensation recognizable is 

 afforded by what happens when we laugh. When 

 people are tickled, they quickly burst into laughter, 

 and this is because the motion quickly penetrates to 

 this part, and even though it is only gently warmed, 

 still it produces a movement (independently of the 

 will) in the intelligence which is recognizable. The 

 fact that human beings only are susceptible to 

 tickling is due (1) to the fineness of their skin and 

 (2) to their being the only creatures that laugh. Tick- 

 ling means, simply, laughter produced in the way I 

 have described by a movement applied to the part 

 around the armpit. 



It is said that when in Λvar men are struck in the 

 part around the diaphragm, they laugh « on ac- 

 count of the heat which arises owing to the bloAv. 



281 



