7. The blood found in the arteries is red; that in the veins is dark
blue or purple.

8. The color of the blood changes from red to blue in going through the
capillaries. The change is due to the loss of oxygen.

9. In the circulation of the lungs, the blood in the arteries is blue,
that in the veins, red.

10. The change from blue to red takes place while the blood is passing
through the capillaries of the lungs. The change is due to the oxygen
which the corpuscles of the blood take up in the lungs.

11. The pulse is caused by the beating of the heart.

12. The heart does a great deal of work every day in forcing the blood
into different parts of the body.

13. Some of the white blood corpuscles escape from the blood-vessels
through the thin walls of the capillaries.

14. These corpuscles return to the heart through small vessels called
lymph channels or lymphatics.

15. The lymphatics in many parts of the body run into small roundish
bodies called lymphatic glands.

16. The object of the lymphatics is to remove from the tissues and
return to the general circulation the lymph and white blood corpuscles
which escape through the walls of the capillaries.