meeting with the fresh air in the lungs, it is carried all over the body by means of the arteries, Figure 7, a. In its course, it gives out warmth, and strength, and life, and by the time it gets into the veins, v, it is quite dark and bad again. When the , web of a frog's foot is placed under the microscope, the blood can be seen, as in Figure 7, going from the artery a into the vein v, changing its colour, and FIGURE 7. becoming impure, just as it does when it goes through the arms, legs, head, and body of man; when it has become bad, it goes to the lungs, to be made pure and of a bright red colour again; for this reason the lungs ought to be in a very good state, as they have very important work to do, and if they cannot do their work well, bad health must follow. i 10. If we look at the drawing of the finger, Figure 8, we shall see how the blood from the artery a, when it gets to the end of the finger, enters the small vessels i; the capillaries or vessels between the arteries and veins, (therefore called intermediate) from which the vein v takes its rise, to carry the dark blood back to the heart and lungs. In Fi- FIGURE 8. gure 8, the artery is placed on one side of the finger, and the vein on the other, in order to show well the way in which the blood goes from the artery into the vein; in the living finger there really is an artery and a vein on each side, and all over the body these two vessels are placed close to each other, sometimes so near as to be difficult to separate. In Figures 9 and 10 the arteries and veins are supposed to be separated from each other, and a drawing is made of each in this state, because in reality the two are so bound together, one sometimes being in front of and concealing the other, that it would have been impossible to show both in one Figure. a a 11. In Figure 9, the pipes or vessels called arteries are shown, which commence at the heart H, and carry FIGURE 9. the pure blood all over the body; the course of the blood is seen by the way the arrows are directed. |