ement, while the
subsequent contraction is slow and interrupted."--Bowditch's _Hints for
Teachers of Physiology_.

[Illustration: Fig. 83.--How the Pulse may be studied by Pressing a
Mirror over the Radial Artery.]

Experiment 103. _To illustrate the effect of muscular exercise in
quickening the pulse_. Run up and down stairs several times. Count the
pulse both before and after. Note the effect upon the rate.

Experiment 104. _To show the action of the elastic walls of the
arteries._ Take a long glass or metal tube of small caliber. Fasten one
end to the faucet of a water-pipe (one in a set bowl preferred) by a
very short piece of rubber tube. Turn the water on and off alternately
and rapidly, to imitate the intermittent discharge of the ventricles.
The water will flow from the other end of the rubber pipe in jets, each
jet ceasing the moment the water is shut off.

The experiment will be more successful if the rubber bulb attached to an
ordinary medicine-dropper be removed, and the tapering glass tube be
slipped on to the outer end of the rubber tube attached to the faucet.

Experiment 105. Substitute a piece of rubber tube for the glass
tube, and repeat the preceding experiment. Now it will be found that a
continuous stream flows from the tube. The pressure of water stretches
the elastic tube, and when the stream is turned off, the rubber recoils
on the water, and the intermittent flow is changed into a continuous
stream.

Experiment 106. _To illustrate some of the phenomena of
circulation._ Take a common rubber bulb syringe, of the Davidson,
Household, or any other standard make. Attach a piece of rubber tube
about six or eight feet long to the delivery end of the syringe.

To represent the resistance made by the capillaries to the flow of
blood, slip the large end of a common glass medicine-dropper into the
outer end of the rubber tube. This dropper has one end tapered to a fine
point.

Place the syringe flat, without kinks or bends, on a desk or table.
Press the bulb slowly and regularly. The water is thus pumped into the
tube in an intermittent manner, and yet it is forced out of the tapering
end of the glass tube in a steady flow.

Experiment 107. Take off the tapering glass tube, or, in the place
of one long piece of rubber tube, substitute several pieces of glass
tubing connected together by short pieces of rubber tubes. The o