Everywhere around us, there are millions of tiny living things called germs. They are so tiny that they can be seen only under the most powerful microscope. Some of these germs are no wider than twenty-five thousandth of an inch!

Louis Pasteur, the great French scientist, was the first to prove that germs exist. The germs in the air can be counted. The number of germs around us, especially in crowded rooms, is tremendous. Certain scientists counted 42,000 germs in approximately one cubic meter of air in a picture gallery when it was empty. But when the gallery was crowded with people, they found nearly 5,000,000 germs in the same place. In the open air germs are less abundant. There are fewer germs in country air than in town air. We see at once how important it is, therefore, to live as much as possible in the open air, and for the rooms we live in to always be well ventilated by fresh air.

What is the purpose of the passage above?