Juvenile literature History 20 Nutrition 16 Biography 15 Experiments 9 Food 9 Medicine 9 Agriculture 8 Body, Human 8 Aeronautics 7 Airplanes 6 Health 6 Human anatomy 6 Inventions 6 Machinery 6 Technology 6 Airplanes, Military 5 Blood 5 Circulation 5 Diet 5 Artificial satellites 4 Body, human 4 Bombers 4 Children 4 Flight 4 Fruit 4 Human physiology 4 Inventors 4 Miscellanea 4 Pictorial works 4