How does the brain send messages to the different parts of the body?
What does the blood take up from the body?
What becomes of food after it is swallowed?
How are the bones of a child different from those of a grown person?
How does it hurt the bones to sit or stand badly?
Why is it hurtful to carry them on the hip?
Many years ago there was a wise governor-general in the Philippine Islands, who left a large sum of money to the city of Manila. This money was to be put out at interest and allowed to increase, and in his will the governor-general directed that when there should be a large enough sum, it should be used to build waterworks for the city of Manila.
The waterworks were not built until a hundred years after the governor-general died. In 1872 another wise governor-general came to the islands, and learning of this money which had been left, he at once set to work to provide the city with a water supply. This was one of the best things that ever happened to Manila. In the tropics nothing is more important than pure water.
There is a great deal of water in the body. In fact, three fourths of the body is made up of water. It is in the blood, in the muscles, and in the bones. There is even some water in the enamel of the teeth, which is the hardest substance in the whole body. The digestive juices, the saliva, and the different intestinal juices, all help to dissolve some part of the food which we take. To obtain this power to dissolve the food, they depend upon water.
When a man is thirsty, it seems to him that his throat is dry. But dryness of the throat is only a sign by which the body makes known its need. Thirst is the cry of the fluids and tissues for water. It means that some part of the body is suffering for the precious fluid.
If we look at a drop of water under a microscope, which magnifies it many times, we shall see in the water a great number of moving specks which are really little animals. The animals are so small that thousands of them can live in a single drop of water as happily as they could in a whole ocean of room. They are called germs. Some of them are wholesome: they help to keep the water bright and sparkling and sweet, and make it pleasant to the taste. But some of them are very harmful: they produce many kinds of disease, most of which cause death.