Window screens. Houseflies are irritating today, but they used to be major vectors of deadly diarrheal disease. Clean water and treatment of sewage eliminated the most obvious means of transmitting these diseases, but pesky houseflies continued to spread deadly microbes. By the 1920s, according to James Riley in "Rising Life Expectancy: A Global History," a growing aversion to insects and the introduction of window screens reduced this risk.
The discovery of unconscious bias. The reason we trust double-blind, placebo-controlled clinical trials to tell us which medical treatments actually work is that we know we can't trust ourselves. If you take a sham drug that you think will alleviate your symptoms, it will — that's the placebo effect. If you think the drug will cause side effects, it will — that's the nocebo effect. If you're a clinician and think you're administering a real drug, you will send all kinds of signals, unintentionally, to tell the patient you think the treatment will work. If you've seen anecdotal evidence for a treatment, you notice confirmatory evidence rather than cases that make you revise your original hypothesis. When analyzing the data, it's all too easy to squint at the numbers in a way that confirms your expectations. Double-blind trials overcome these biases by preventing both patient and clinician from knowing whether a tested drug is real or not.
Botts' Dots. Those raised ceramic reflectors between road lanes were invented by Elbert Botts, a chemist who worked for the California Department of Transportation. The dots help motorists see the edge of their lane even in the dark or when it's raining. Botts died in 1962, four years before the first Botts' dots were installed on California highways.
Morbidity and Mortality Weekly Report. That's the no-nonsense name of one of the most important publications most people have never heard of. The Centers for Disease Control and Prevention has been publishing it since 1952 to provide "timely, reliable, authoritative, accurate, objective, and useful public health information and recommendations." When a new disease or danger emerges — such as AIDS or a new strain of influenza — the MMWR is often the first to identify it.