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
areas in question from altered supply of blood is reasonably
certain. As a consequence of this summation-process there would
result in many cases and in cases of excessive nervous discharge
the opposite of pleasure, namely: pain. A number of instances
have been recorded of death resulting from tickling, and there is
no reason to doubt the truth of the statement that Simon de
Montfort, during the persecution of the Albigenses, put some of
them to death by tickling the soles of their feet with a feather.
An additional causal factor in the production of tickling may lie
in the nature and structure of the nervous process involved in
perception in general. According to certain histological
researches of recent years we know that between the sense-organs
and the central nervous system there exist closely connected
chains of conductors or neurons, along which an impression
received by a single sensory cell on the periphery is propagated
avalanchelike through an increasing number of neurons until the
brain is reached. If on the periphery a single cell is excited
the avalanchelike process continues until finally hundreds or
thousands of nerve-cells in the cortex are aroused to
considerable activity. Golgi, Ramon y Cajal, Koelliker, Held,
Retzius, and others have demonstrated the histological basis of
this law for vision, hearing, and smell, and we may safely assume
from the phenomena of tickling that the