Chap. VIII. LAUGHTER. 199 



danger, were particularl} T apt to burst out into loud 

 laughter at the smallest joke. So again when young 

 children are just beginning to cry, an unexpected event 

 will sometimes suddenly turn their crying into laughter, 

 which apparently serves equally well to expend their 

 superfluous nervous energy. 



The imagination is sometimes said to be tickled by a 

 ludicrous idea; and this so-called tickling of the mind 

 is curiously analogous with that of the body. Every one 

 knows how immoderately children laugh, and how their 

 whole bodies are convulsed when they are tickled. The 

 anthropoid apes, as we have seen, likewise utter a re- 

 iterated sound, corresponding with our laughter, when 

 they are tickled, especially under the armpits. I touched 

 with a bit of paper the sole of the foot of one of my 

 infants, when only seven days old, and it was suddenly 

 jerked away and the toes curled about, as in an older 

 child. Such movements, as well as laughter from being 

 tickled, are manifestlv reflex actions; and this is like- 

 wise shown by the minute unstriped muscles, which 

 serve to erect the separate hairs on the body, contract- 

 ing near a tickled surface. 6 Yet laughter from a ludi- 

 crous idea, though involuntary, cannot be called a strict- 

 ly reflex action. In this case, and in that of laughter 

 from being tickled, the mind must be in a pleasurable 

 condition; a voung child, if tickled by a strange man, 

 would scream from fear. The touch must be light, and 

 an idea or event, to be ludicrous, must not be of grave 

 import. The parts of the body which are most easily 

 tickled are those which are not commonly touched, such 

 as the armpits or between the toes, or parts such as the 

 soles of the feet, which are habitually touched by a broad 



8 J. Lister in ' Quarterly Journal of Microscopical Sci- 

 ence,' 1853, vol. i. p. 266. 



