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 sense of touch is not
lacking in a similar arrangement. May not a suggestion be
offered, with some plausibility, that even in ideal or
representative tickling, where tickling results, say, from
someone pointing a finger at the ticklish places, this
avalanchelike process may be incited from central centres, thus
producing, although in a modified degree, the pleasant phenomena
in question? As to the deepest causal factor, I should say that
tickling is the result of vasomotor shock.
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