8. The scales form the nails on the ends of the fingers.
9. The scales also form the hair.
CHAPTER XII
THE NERVES, SPINAL CORD, AND BRAIN
136. Need of nerves.—The cells of the mouth, stomach, and intestine digest food; the cells of the liver change the food to blood; the cells of the heart pump the blood to feed all the cells of the body; the red blood cells carry air for the cells to breathe; and the cells of the skin and kidneys carry away the waste of the rest of the cells. Each set of cells works for all the rest. If the cells of the body were only tied together, each one would do as it pleased, and no two would work together. But something tells each cell of the body to work with the others. The cells all obey the mind. A tiny thread goes to each cell of the body. Each thread is a nerve. The mind and the cells signal to each other over the nerves. By means of the nerves the mind makes the cells work together.
A nerve thread (×400).
a central conducting fiber. b covering of fat.