Injuries of nerves and their consequences - Reflex Sympathetic ...

SEXSORY LESIONS. 183
thesias, and cramped positions of tlie part from muscular
atrophies and joint-disease.
For numeral appreciations, we make use of the sesthesiometer,
which consists of a compass the points of which are
covered with little rounded balls, a scale placed above enabling
us to learn how far apart are the points.* There is
a more convenient form of instrument, in which the two
limbs of the compass slide upon a graduated bar. With
its aid we desire to learn what is the least distance at
which the separated points can be distinguished as two.
When nearer than this, they are felt only as one. Weber
has given very full tables for all parts of the skin, stating
the distances at which the two points are normally distinguished
as a single point. Unfortunately, these are
of limited value in diseased states, because the individual
sensory capacity varies remarkably, so that it is always
necessary to compare the part with a corresponding
portion of healthy skin in order to get a normal standard.
Even with this aid, the use of the sesthesiometer
is not so easy or simple as might be supposed. The
answers often vary when you repeat the observation at
the same place a few minutes later, and in children or
unintelligent patients the records thus obtained have but
little utility.
These are intrinsic difficulties which have
somewhat lessened the practical value of the sesthesioraeter.
The precautions requisite to give to its answers all
possible truthfulness are these: the patient's eyes should
be covered, and the part to be examined should be at rest,
and the compass-points, which ought to be rounded,
should be lightly placed on the skin, taking care to let
both come down with equal force and at once,
since otherwise
the succession of impressions informs the patient that
* Ordinary compasses, and a rule on which to ascertain the extent of
separation of their parts, answer every purpose.