Mark Meester, age 11, of Gallup, N.M., for his question:

HOW DO THEY MAKE PENICILLIN?

Penicillin is a wonder drug that wipes out many types of infectious bacteria. It is classed as an antibiotic because it destroys germs without damaging living tissues. This lifesaver is created by tiny penicillin molds as they convert their chemical nutrients into useful food. Spores of the mold are put into a soupy broth  where they thrive and multiply.

Nowadays, most penicillin is made by the deep culture method. From 10,000 to 15,000 gallons of the special broth are prepared in an enormous super clean tank. Into this goes a helping of the penicillin mold. The whole thing is agitated by air bubbles and kept at the right temperature.The molds thrive and multiply deep in the tank, adding their wonder drug to the broth. Finally the molds are removed. The broth is dried and the solids are refined and purified, leaving only the powdery penicillin. Hundreds of tons of this wonder drug are made every year by this deep culture method.