is the cause of these
changes?

10. If the oxygen and hemoglobin formed a strong instead of a weak
chemical union, could the hemoglobin then act as an oxygen carrier? Why?

11. What habits of living favor the development of corpuscles in the
blood?

12. Why will keeping the skin clean and active improve the quality of
one's blood?

PRACTICAL WORK

*To demonstrate the Physical Properties of Blood* (Optional).--Since blood
is needed in considerable quantity in the following experiments, it is
best obtained from the butcher. To be sure of securing the blood in the
manner desired, take to the butcher three good-sized bottles bearing
labels as follows:

*1* Fill two thirds full. While the blood is cooling, stir rapidly with
the hand or a bunch of switches to remove the clot.

*2* Fill two thirds full and set aside without shaking or stirring.

*3* Fill two thirds full and thoroughly mix with the liquid in the bottle.

Label 3 must be pasted on a bottle, having a tight-fitting stopper, which
is filled one fifth full of a saturated solution of Epsom salts. The
purpose of the salts is to prevent coagulation until the blood is diluted
with water as in the experiments which follow.

*Experiments.*--1. Let some of the defibrinated blood (bottle 1) flow (not
fall) on the surface of water in a glass vessel. Does it remain on the
surface or sink to the bottom? What does the experiment show with
reference to the relative weight of blood and water?

2. Fill a large test tube or a small bottle one fourth full of the
defibrinated blood and thin it by adding an equal amount of water. Then
place the hand over the mouth and shake until the blood is thoroughly
mixed with the air. Compare with a portion of the blood not mixed with the
air, noting any difference in color. What substance in the air has acted
on the blood to change its color?

3. Fill three tumblers each two thirds full of water and set them in a
warm place. Pour into one of the tumblers, and thoroughly mix with the
water, two tablespoonfuls of the blood containing the Epsom salts. After
an interval of half an hour add blood to the second tumbler in the same
manner, and after another half hour add blood to the third. The water
dilutes the salts so that coagulation is no longer prevented. Jar the
vessel occasionally as coagulation proceeds; and if the clot is slow in
forming, add a trace of some salt of calcium (calcium chloride). After the
blood has been add