oval structures into each of which many lymphatic vessels are found to
run, as shown in the illustration. These are called _lymphatic glands_.

[Illustration: LYMPH GLAND AND VESSELS.]

~16.~ The heart and blood-vessels are among the most wonderful
structures in the body. It is no wonder, then, that alcohol, tobacco,
and other narcotics and stimulants produce their most deadly effects
upon these delicate organs. What these effects are we shall learn more
fully in the next chapter.


SUMMARY.

1. The heart beats to circulate the blood.

2. The heart has four chambers, two upper and two lower.

3. There are tubes called blood-vessels which carry the blood to all
parts of the body.

4. These tubes are connected with the heart.

5. The vessels which carry blood away from the heart are called
arteries, and those which carry blood back to the heart are called
veins.

6. The arteries and veins are connected by small tubes called
capillaries.