Experiment 97. Wash away the coloring matter from the twigs (see Experiment 89) with a stream of water until the fibrin becomes quite white. It is white, fibrous, and elastic. Stretch some of the fibers to show their extensibility; on freeing them, they regain their elasticity. Experiment 98. Take some of the serum saved from Experiment 88 and note that it does not coagulate spontaneously. Boil a little in a test tube over a spirit lamp, and the albumen will coagulate. Experiment 99. _To illustrate in a general way that blood is really a mass of red bodies which give the red color to the fluid in which they float._ Fill a clean white glass bottle two-thirds full of little red beads, and then fill the bottle full of water. At a short distance the bottle appears to be rilled with a uniformly red liquid. Experiment 100. _To show how blood holds a mineral substance in solution_. Put an egg-shell crushed fine, into a glass of water made acid by a teaspoonful of muriatic acid. After an hour or so the egg-shell will disappear, having been dissolved in the acid water. In like manner the blood holds various minerals in solution. Experiment 101. _To hear the sounds of the heart_. Locate the heart exactly. Note its beat. Borrow a stethoscope from some physician. Listen to the heart-beat of some friend. Note the sounds of your own heart in the same way. Experiment 102. _To show how the pulse may be studied_.“The movements of the artery in the human body as the pulse-wave passes through it may be shown to consist in a sudden dilatation, followed by a slow contraction, interrupted by one or more secondary dilatations. This demonstration may be made by pressing a small piece of looking-glass about one centimeter square (⅔ of an inch) upon the wrist over the radial artery, in such a way that with each pulse beat the mirror may be slightly tilted. If the wrist be now held in such a position that sunlight will fall upon the mirror, a spot of light will be reflected on the opposite side of the room, and its motion upon the wall will show that the expansion of the artery is a sudden movement, 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.