THE SKIN AS AN ORGAN OF SENSE. BBL 
sensations, when these give rise to affections of the central 
nervous cells resulting in (1) perceptions and (2) judgments, 
when we take into account the psychic processes; and, from the 
nature of cell-life generally, we must recognize a certain inten- 
sity of the stimulus necessary to arouse a sensation and a limit 
within which alone we have power to discriminate (range of 
stimulation and perception); and also a limit to the rapidity 
with which stimuli may succeed each other to any advantage, 
so as to give rise to new sensations; and a limit to the endur- 
ance of the apparatus in good working condition corresponding 
to clear mental perceptions, together with the value of past ex- 
perience in the interpretation of our sensations, 
THE SKIN AS AN ORGAN OF SENSE. 
Bearing in mind that all the sensory organs originate in 
the ectoderm, we find in the skin even of the highest animals 
the power to give the central nervous system such sense-im- 
pressions as bear a relation to the original undifferentiated 
sensations of lower forms as derived from the general surface 
of the body, but with less of specialization than is met with in 
the sense of hearing and vision; so that it is possible to under- 
stand how it is that the skin must be regarded not only as the 
original source of sensory impulses for the animal kingdom, 
but why it still remains perhaps the most important source of 
information in regard to the external world, and the condition 
of our own bodies; for it must be remembered that the data 
afforded for sensory judgments by all the other senses must 
be interpreted in the light of information supplied by the skin. 
We really perceive by the eye only retinal images. The dis- 
tance, position, shape, etc., of objects are largely determined by 
feeling them, and thus associating with a certain visual sensa- 
tion others derived from the skin and the muscles, which latter 
are, however, generally also associated with tactile sensations. 
It is recorded of those blind from birth that, when restored 
to sight by surgical operations, they find themselves quite 
unable to interpret their visual sensations; or, in other words, 
seeing they do not understand, but must learn by the other 
senses, especially tactile sensibility, what is the real nature of 
the objects that form images on their retine. All objects seen 
appear to be against the eyes, and any idea of distance is out 
of the question. 
