of Eclinburgli, Session 1883 - 84 . 
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tion of the value of these factors is all the more necessary, as they 
are hopelessly confounded in most works on mental science. 
We have, first, the irritation of the peripheral sensitive nerve; 
secondly, the transmission of some change thus produced in the 
nerve ; and thirdly, that effect produced upon centrally placed 
nerve-cells associated with the production of feeling, and a con- 
sciousness of that feeling. The time elapsing between the impact 
of a body on the hand and the consciousness of that impact is much 
less than between the application of a drop of sugar solution to the 
tongue and the resulting sensation of sweetness. This period is 
different in the case of each sensation. On what does this depend ? 
I shall endeavour to show that the dependence is not mainly on 
differences of time taken by the impression to pass along different 
nerves, nor need we look to differences affecting central cells ; but 
we have, in the nature of the stimulus applied and in that of the 
stimulated end-organ, a cause which will account for everything. 
Herbert Spencer, in his Principles of Psychology (vol. i. p. 169, 
third edition), would actually distinguish between peripherally 
initiated feelings caused by internal disturbances — some of which, 
he says, are extremely indefinite, and few or none definite in a high 
degree — and feelings caused by external disturbances which are 
mostly related quite closely, alike by coexistence and sequence, 
among the highest of them the mutual limitations in time and space 
or both being extremely sharp. He illustrates this by the fact that 
our states of consciousness in connection with vision and hearing 
are more sharply limited in time and space than those in connection 
with smell and taste, and, still more, hunger. 
How, discarding the fact that when considered developmentally 
the retina at any rate is far more interjial than the mouth and 
nose, the former being really a portion of the brain, the latter 
puckerings-in of the surface, I would suggest, that the all-import- 
ant factor producing this difference, is not the brain, or the pro- 
duced feelings, as Herbert Spencer seems to me to indicate, but the 
nature of the peripheral end-organ stimulated. If the point of a 
pin impinges upon the fingertip, the epithelium is depressed, and at 
the same time the nerves of tactile sensibility are stimulated ; and 
on withdrawing the pin, they are at that moment unstimulated, 
and in a condition of rest. Also in the ear, the sound vibrations 
