gain, thus securing a number of records of the
results for both hot and cold over a given area. He chose an area of
skin on the forearm, shaved it carefully, and proceeded to explore it
with the smallest points of metals which could be drawn along the skin
without pricking or tearing. These points were attached to metallic
cylinders, and around the cylinders rubber bands were placed; the
cylinders were then thrust in hot or cold water kept at certain
regular temperatures, and lifted by the rubber bands. They were placed
point down, with equal pressure, upon the points of the skin in the
area chosen. In this way, points which responded only to hot, and also
those responding only to cold, were found, marked with delicate ink
marks in each case, until the whole area was explored and marked in
different colours. This had often been done before. It remained to
devise a way of keeping these records, so that the markings might all
be removed from the skin, and new explorations made over the same
surface. This was necessary in order to see whether the results
secured were always the same. The theory that there were certain
nervous endings in the skin corresponding to the little points
required that each spot should be in exactly the same place whenever
the experiment was repeated.

[Footnote 3: Mr. J. F. Crawford, graduate student.]

Mr. C. made a number of so-called "transparent transfer frames." They
are rectangular pieces of cardboard, with windows cut in them. The
windows are covered with thin architect's paper, which is very
transparent. This frame is put over the forearm in such a way that the
paper in the window comes over the markings made on the arm. The
markings show through very clearly, and the points are copied on the
paper. Then certain boundary marks at the corners are made, both on
the paper and on the arm, at exactly the same places, the frame is
removed, and all the markings on the arm are erased except the
boundary points. The result is that at any time the frames can be put
over the arm again by matching the boundary points, and then the
original temperature spots on the skin will be shown by the markings
on the paper window.

Proceeding to repeat the exploration of the same area in this way, Mr.
C makes records of many groupings of points for both hot and cold
sensations on the same area; he then puts the frames one upon another,
holds them up before a window so that they have a bright background,
and i