Experiment 162.  Use a small pair of wooden compasses, or an ordinary pair of dividers with their points guarded by a small piece of cork.  Apply the points of the compasses lightly and simultaneously to different parts of the body, and ascertain at what distance apart the points are felt as two.  The following is the order of sensibility:  tip of tongue, tip of the middle finger, palm, forehead, and back of hand.

Experiment 163.  Test as in preceding experiment the skin of the arm, beginning at the shoulder and passing downwards.  Observe that the sensibility is greater as one tests towards the fingers, and also in the transverse than in the long axis of the limb.  In all cases compare the results obtained on both sides of the body.

  Experiment 164.  By means of a spray-producer, spray the back of the
  hand with ether, and observe how the sensibility is abolished.

Experiment 165.  Touch your forehead with your forefinger; the finger appears to feel the contact, but on rubbing the forefinger rapidly over the forehead, it is the latter which is interpreted as “feeling” the finger.

Experiment 166.  Generally speaking, the sensation of touch is referred to the cutaneous surfaces.  In certain cases, however, it is referred even beyond this.  Holding firmly in one hand a cane or a pencil, touch an object therewith; the sensation is referred to the extremity of the cane or pencil.

If, however, the cane or pencil be held loosely in one’s hand, one experiences two sensations:  one corresponding to the object touched, and the other due to the contact of the rod with the skin.  The process of mastication affords a good example of the reference of sensations to and beyond the periphery of the body.

Experiment 167.  Prepare a strong solution of sulphate of quinine with the aid of a little sulphuric acid to dissolve it (bitter), a five-per-cent solution of sugar (sweet), a ten-per-cent solution of common salt (saline), and a one-per-cent solution of acetic acid (acid).  Wipe the tongue dry, and lay on its tip a crystal of sugar.  It is not tasted until it is dissolved.

  Experiment 168.  Apply a crystal of sugar to the tip, and another to
  the back of the tongue.  The sweet taste is more pronounced at the tip.

Experiment 169.  Repeat the process with sulphate of quinine in solution.  It is scarcely tasted on the tip, but is tasted immediately on the back part of the tongue.  Test where salines and acids are tasted most acutely.

  Experiment 170. To illustrate the muscular sense.  Take two equal
  iron or lead weights; heat one and leave the other cold.  The cold weight
  will feel the heavier.