7. “Corpuscles of the blood.” Minute particles, both red and white, existing in the blood, which can be seen under a microscope. In the human species the red corpuscles are thick and circular. They are so small that Young says it would take 255,000 of them to cover a surface of a square inch. They are elastic and pliant, so that they can pass through blood vessels having a smaller diameter than themselves. The white corpuscles are more globular than the red, and contain more fat, and have the power of changing their form. These spontaneous changes have been thought by some scientists a proof that they are microscopic animals. But this is scarcely a sufficient reason for admitting that they are animalculæ, as the muscles of a body, when separated from it, often manifest apparently spontaneous movements. 8. Phosphoric acid is always produced by burning phosphorus in air or oxygen. The experiment may be performed as follows, but before undertaking it see page 167 of the “Chemistry,” and note with how much care it must be handled: Place a fragment of carefully dried phosphorus in a small cup on a stand in the middle of a large plate, ignite it by a hot wire, and place over it a bell-glass. White fumes will fill the glass and aggregate into small particles, which will fall to the plate, presenting the appearance of a miniature snow storm. 9. Barium is a yellow, lustrous, malleable metal. It is used in fireworks, for the green color it gives off in burning. 10. “Bayberries.” The plant, called also wax myrtle, is a low, crooked shrub found throughout the United States, especially near the sea coast. It grows to a height of from three to eight feet. The naked flowers appear in April and May, in clusters, of which from four to nine ripen into dry berries. Plantations of them have long been cultivated in Europe, and they have been raised in Algeria. For many years they have been an article of commerce. A bushel of the berries will yield from four to five pounds of wax. 11. “Strontium.” It takes its name from Strontian, in Scotland, where it was first observed as a carbonate. It is a pale yellow metal, harder than lead. If strontium carbonate be dissolved in nitric acid and mixed with combustible substances it will burn with a beautiful carmine red flame, and for this purpose is much used in fireworks. 12. “Sodium.” See “Chemistry,” page 67. It is a lustrous, silver-white, soft metal. When thrown upon water, if it be prevented from moving, or if the water be warm, it ignites, burning with its characteristic yellow flame. 13. Extinguishing flame by carbon di-oxide. See “Chemistry,” page 218.