_Experiment 2._ =Does Gravity affect the Blood Flow?=--Hold the right hand above the head for a few minutes. At the same time let the left hand hang straight down. Then bring the hands together and see which is of a darker red because of containing more blood. Now reverse the position of the hands for a few minutes, and find whether the effect is reversed. (Entire class.) _Experiment 3._ =Study of Human Blood.=--Examine a drop of blood under the microscope, first diluting it with a little saliva. See Fig. 60. _Experiment 4._ =The Circulation in a Frog.=--Wrap a small frog in a moist cloth, lay on a slip of glass, place under the microscope, and study the circulation in the web of its foot. _Experiment 5._ (Entire class.) =Effect of Exercise upon the Pulse.=--Tap a bell as the second hand of a watch begins a minute and let the pupils count the pulse at the radial artery on the wrist above base of thumb. Repeat standing, or after gymnastics or recess. Result? _Experiment 6._ =The Action of the Valves in the Veins.=--Place the tip of the middle finger on one of the large veins of the wrist; with the forefinger then stroke the vein toward the elbow so as to push the blood from a portion of it, keeping both fingers in place. The vein remains empty between the fingers. _Lift the finger nearer the heart and no blood enters the vein; there is a valve above which holds it back. Lift the other finger and the vein fills instantly._ Stroke a vein toward the hand, and notice that the veins swell up into little knots where the valves are. Stroke in the reverse direction. Result? _Experiment 7._ =Finding the Capillary Pressure.= This is found by pressing a glass plate or tumbler upon a red part of the skin. When the skin becomes pale the capillary pressure is counterbalanced. _Experiment 8._ =Emergency Drill.=--Let one pupil come forward, mark with blue chalk or pencil the position on his arm of a supposedly cut vein. Let another pupil use means to stop the imagined blood flow. _Experiment 9._ Let another pupil stop the flow from an imaginary cut artery marked red. See text. _Experiment 10._ In a case of nose bleed do not let pupil lean over a bowl. (Why?) Cause him to stand rather than lie. (Why? See Exp. 2.) Apply cold water to contract arteries to nose, also have pupil hold a small roll of paper or a coin under upper lip (to make muscular pressure on arteries to nose). _Experiment 11._ Let one pupil treat another for a bruise (see p. 62). _Experiment 12._ Emergency drill, restoration from fainting (see p. 57).