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Table of contents
PREFACE
TOUCH-1
TOUCH-2
TOUCH-3 (begin)
TOUCH-3 (end)
TOUCH-4 (begin)
TOUCH-4 (end)
SMELL-1
SMELL-2
SMELL-3.1
SMELL-3.2
SMELL-3.3
SMELL-3.4
SMELL-3.5
SMELL-4 (begin)
SMELL-4 (end)
SMELL-5
HEARING-1
HEARING-2
HEARING-3
VISION-1.1
VISION-1.2
VISION-1.3
VISION-2.1
VISION-2.2
VISION-2.3
VISION-2.4
VISION-3
VISION-4
VISION-5
APPENDIX A
APPENDIX B HISTORY-1
APPENDIX B HISTORY-2.1
APPENDIX B HISTORY-2.2
APPENDIX B HISTORY-2.3
APPENDIX B HISTORY-3.1
APPENDIX B HISTORY-3.2
INDEX OF AUTHORS

regions, such as the sole of the foot, the knee, the sides, which already 

exists before birth, has for its object the excitation and preservation of 

the muscular movements necessary to keep the foetus in the most favorable 

position in the womb.[10] It is, in fact, certainly the case that the 

stimulation of all the ticklish regions in the body tends to produce 

exactly that curled up position of extreme muscular flexion and general 

ovoid shape which is the normal position of the foetus in the womb. We may 

well believe that in this early developed reflex activity we have the 

basis of that somewhat more complex ticklishness which appears somewhat 

later. 

 

The mental element in tickling is indicated by the fact that even a child, 

in whom ticklishness is highly developed, cannot tickle himself; so that 

tickling is not a simple reflex. This fact was long ago pointed out by 

Erasmus Darwin, and he accounted for it by supposing that voluntary 

exertion diminishes the energy of sensation.[11] This explanation is, 

however, inadmissible, for, although we cannot easily tickle ourselves by 

the contact of the skin with our own fingers, we can do so with the aid of 

a foreign body, like a feather. We may perhaps suppose that, as 

ticklishness has probably developed under the influence of natural 

selection as a method of protection against attack and a warning of the 

approach of foreign bodies, its end would be defeated if it involved a 

simple reaction to the contact of the organism with itself. This need of 

protection it is which involves the necessity of a minimal excitation 

producing a maximal effect, though the mechanism whereby this takes place 

has caused considerable discussion. We may, it is probable, best account 

for it by invoking the summation-irradiation theory of pain-pleasure, the 

summation of the stimuli in their course through the nerves, aided by 

capillary congestion, leading to irradiation due to anastomoses between 

the tactile corpuscles, not to speak of the much wider irradiation which 

is possible by means of central nervous connections. 

 

Prof. C.L. Herrick adopts this explanation of the phenomena of 

tickling, and rests it, in part, on Dogiel's study of the tactile 

corpuscles ("Psychological Corollaries of Modern Neurological 

Discoveries," _Journal of Comparative Neurology_, March, 1898). 

The following remarks of Prof. A. Allin may also be quoted in 

further explanation of the same theory: "So far as ticklishness 

is concerned, a very important factor in the production of this 

feeling is undoubtedly that of the summation of stimuli. In a 

research of Stirling's, carried on under Ludwig's direction, it 

was shown that reflex contractions only occur from repeated 

shocks to the nerve-centres--that is, through summation of 

successive stimuli. That this result is also due in some degree 

to an alternating increase in the sensibility of the various 


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