1. To show that air is warmed by breathing, breathe for a few seconds on the bulb of a thermometer. The mercury will be seen to rise rapidly in the stem.

2. To demonstrate that air gains water in the lungs, breathe on a mirror, or on a knife-blade or other polished metallic surface.

8. The presence of carbon dioxide in expired air may be readily demonstrated by expiring through a tube immersed in lime-water. This may be obtained at any drug-store; with carbon dioxide it gives a white precipitate, which dissolves readily in a little vinegar.

4. To show that much less carbon dioxide exists in inspired air, take a small bottle with a wide neck. Fit tightly into the neck of the bottle a cork perforated by two holes. Through one hole pass a glass tube reaching to near the bottom of the bottle, and through the other one which ends just below the cork; on the outer end of this tube fit a foot or so of rubber tubing. Remove the cork; half fill the bottle with lime-water and then replace the cork. Suck air through the rubber tubing. It will bubble through the lime-water, but (unless the room is very badly ventilated) a great deal must be drawn through the lime-water before as abundant a precipitate is produced as that which results from blowing a small quantity of breathed air (3) through the lime-water.

5. The influence of oxygen upon the color of the blood may be illustrated as follows: a. Take to a slaughter-house a glass jar or beaker (an ordinary tumbler answers quite well), two bottles, an earthenware quart pitcher, and a bundle of wire.

b. When an animal is killed and bled, collect some blood in the jar and let it clot.

c. Collect some more blood in the pitcher, and defibrinate by thorough whipping with the bundle of wire. Half fill each bottle with the defibrinated blood; then cork the bottles.

d. Having brought home all the specimens, set them aside until the next morning in a cool place. It will then be found that the blood in each bottle is dark-colored or venous (having used up its own oxygen and not being able to get more from the air), and that the clot in the jar is bright scarlet (arterial-colored) above where it is in contact with the air, but dark purple-red where it is immersed in the serum.

e. Invert the clot: in an hour or two its previously dark original under surface will have become bright red, while the original upper surface, previously bright-colored and now immersed in the serum away from the air, will have become venous in tint.

f. Take the cork out of one bottle; renew the air in it by blowing. Placing a thumb on the neck of the bottle, thoroughly shake up the blood with the air. Then renew the air again, and shake once more; and so on for three or four times. At the end the blood shaken up with air will be seen to have assumed a much brighter red color than that kept shut up in the other bottle.

g. If the proper chemical apparatus and reagents are accessible, the air in the bottle about to be shaken may be replaced by nitrogen, hydrogen, or pure oxygen and the procedures described in section f repeated. It will be found that only the oxygen brightens the blood color. As any one possessing the chemical apparatus and knowledge implied for the execution of this experiment will certainly know how to replace the air by the gases above named, no further details need be given.