How marijuana affects the mind. Marijuana reaches the same pleasure centers in the brain that are targeted by heroin, cocaine and alcohol. Depending on the quantity, quality and method of consumption, marijuana can produce a feeling of euphoria â or high â by stimulating brain cells to release the chemical dopamine.
In 1928, Alexander Fleming made one of the most important contributions to the field of antibiotics. In an experiment, he found that a strain of green Penicillium mold inhibited the growth of bacteria on an agar plate. This led to the development of the first modern era antibiotic, penicillin.
Bacteria usually contaminated the tissue, but Enders' team was now able to get penicillin -- discovered 20 years earlier by Alexander Fleming and developed in the 1940s by Ernst Chain and Howard Florey -- and prevent the bacterial growth. Now viruses like mumps or polio could be created in large quantities for study.