THE SKIN AS AN ORGAN OF SENSE. 553 
festly if there be a sense referable to the muscles (muscular 
sense) at all, when they are contracted at will the impression 
must be clearer than when they but feebly respond to the 
mere pressure of some body. 
It is possible, as every one knows, to attend only to the data 
afforded by one set of impulses, such as those associated with 
our sensations of weight, temperature, etc., but such requires 
special attention; and as in the case of the eye we consider the 
object as a whole, its color, form, size, and other qualities, so 
does the mind form its complete conception by a synthesis or 
union of a variety of sensory data. Regarding the skin as a 
whole, we may speak of the skin-sense as we do of the ocular 
sense or vision. The separate treatment of tactile, thermal, and 
other forms of sensibility under separate headings is a matter 
of convenience; but there is considerable danger that we over- 
look the great fundamental fact that our knowledge of objects 
is primarily synthetic and not analytic. True, in disease, when 
one or more sets of the data of sense as derived from the skin 
is wanting, the others can be appreciated, and these alone. 
Nevertheless, such is an abnormal condition, and in that case 
the outer world passes to a large extent beyond the degree of 
control natural to man. 
Pathological—_It does happen in certain forms of disease, 
notably of the spinal cord, that tactile sensibility is retained 
and thermal lost, or the muscular sense impaired. Such per- 
sons are plainly reduced at once to the condition, not only of 
being without certain sensory impressions, but in consequence 
unable to use others which they do possess to the same extent 
as before. A man with that affection of the spinal cord known 
as locomotor ataxy may have tactile and thermal sensibility, 
yet be unable to use these, in the absence of the muscular sense 
to enable him to be his own master, except when he calls in the 
help of his eyes, as, e. g., in walking. 
It is thus seen how all the various sources of information 
from the skin and muscles blend psychically to produce a 
conception which, as a whole, corresponds to “seeing.” The 
defects just referred to are in a measure comparable to color- 
blindness. 
With this warning we shall now attempt to state some of 
the main facts in regard to the different functions of the skin 
as a sensory organ, especially endeavoring to trace parallel laws 
for this and the other senses. 
