Experiment 95. To make blood transparent or laky.  Place in each of three test tubes two or three teaspoonfuls of defibrinated blood, obtained from Experiment 89, labeled A, B, and C.  A is for comparison.  To B add five volumes of water, and warm slightly, noting the change of color by reflected and transmitted light.  By reflected light it is much darker,—­it looks almost black; but by transmitted light it is transparent.  Test this by looking at printed matter as in Experiment 94.

Experiment 96.  To fifteen or twenty drops of defibrinated blood in a test tube (labeled D) add five volumes of a 10-per-cent solution of common salt.  It changes to a very bright, florid, brick-red color.  Compare its color with A, B, and C.  It is opaque.

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 (2/3 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.]