as in Experiment 106, p. 201.
Take several thin, narrow strips of pine wood. Make little flags by
fastening a small piece of tissue paper on one end of a wooden
toothpick. Wedge the other end of the toothpick into one end of the
strips of pine wood. Use these strips like levers by placing them across
the long rubber tube at different points. Let each lever compress the
tube a little by weighting one end of it with a blackboard eraser or
book of convenient size.

As the pulse-wave passes along under the levers they will be
successively raised, causing a slight movement of the tissue-paper
flags.

Experiment 201. _The dissection of a sheep's heart._ Get a sheep's
heart with the lungs attached, as the position of the heart will be
better understood. Let the lungs be laid upon a dish so that the heart
is uppermost, with its apex turned toward the observer.

The line of fat which extends from the upper and left side of the heart
downwards and across towards the right side, indicates the division
between the right and left ventricles.

Examine the large vessels, and, by reference to the text and
illustrations, make quite certain which are the _aorta_, the _pulmonary
artery_, the _superior_ and _inferior venae cavae_, and the _pulmonary
veins_.

Tie variously colored yarns to the vessels, so that they may be
distinguished when separated from the surrounding parts.

Having separated the heart from the lungs, cut out a portion of the wall
of the _right ventricle_ towards its lower part, so as to lay the cavity
open. Gradually enlarge the opening until the _chordae tendineae_ and the
flaps of the _tricuspid valve_ are seen. Continue to lay open the
ventricle towards the pulmonary artery until the _semilunar valves_ come
into view.

The pulmonary artery may now be opened from above so as to display the
upper surfaces of the semilunar valves. Remove part of the wall of the
right auricle, and examine the right auriculo-ventricular opening.

The heart may now be turned over, and the _left ventricle_ laid open in
a similar manner. Notice that the mitral valve has only two flaps. The
form of the valves is better seen if they are placed under water, and
allowed to float out. Observe that the walls of the _left_ ventricle are
much thicker than those of the _right_.

Open the left auricle, and notice the entrance of the _pulmonary veins_,
and the pass