THE SKIN AS AN ORGAN OF SENSE. 557 
tween the radial side of one finger and the ulnar side of the 
other (Aristotle’s experiment), the subject of the experiment 
being blindfolded, it will be judged as two marbles at first, 
though the tactile impression is soon corrected, especially if the 
.eyes be opened. These surfaces of the fingers have not been 
accustomed to touch at the same time the one body, hence the 
illusion. 
An impression made on the trunk of a nerve is referred to 
the peripheral distribution of that nerve in the skin; thus, if 
the elbow be dipped in a freezing mixture, the skin around the 
joint will experience the sensation of cold, but a feeling of pain 
will be referred to the distribution of the ulnar nerve in the 
hand and arm. The same principle is illustrated by the com- 
mon experience of the effects of a blow over the ulnar nerve, 
the pain being referred to the peripheral distribution; also by 
the fact that pain in the stump of an amputated limb is thought 
to arise in the missing toes, etc. It is said that when skin 
transplanted from the forehead to the nose, to repair missing 
parts, is touched, the sensation is located in the original site 
of the skin (forehead). In all such facts we see how dependent 
are all our sensory judgments on our past experience, illustrat- 
ing the very important truth, with its wide ramifications, that, 
in a physiological sense, as well as in many others, our past 
makes our own future and that of the race to a very large 
extent. 
THE MUSCULAR SENSE. 
Every one must be aware how difficult it is to regulate his 
movements when the limbs are cold or otherwise deadened in 
sensibility. We know too that, in judging of the muscular 
effort necessary to be put forth to accomplish a feat, as throw- 
ing a ball or lifting a weight, we judge by our past experi- 
ence. It is ludicrous to witness the failure of an individual 
to take up a mass of metal which was mistaken for wood. In 
these facts we recognize that in the successful use of the mus- 
cles we are dependent, not alone on the sensations derived from 
the skin, but also from the muscles themselves. True, the mus- 
cles are not very sensitive to pain when cut; it does not, how- 
ever, follow that they may not be sensitive to that different 
effect, their own contraction; whether the numerous Pacinian 
bodies around joints, or the end-organs of the nerves of mus- 
cles are directly concerned, is not determined. 
Pathological. The teaching of disease is plainly indicative of 
