400s BC

Ecology & the environment

Hippocrates of Cos [b. Cos (Kos, Turkey), 460 bce, d. Thessaly, c. 370 bce] observes that a man involved in lead mining developed abdominal cramps. He recommends boiling water to remove pollutants.

The Chinese in Sichuan start using petroleum and natural gas for cooking and lighting, piping gas in bamboo tubes from regions where it arises from the earth and taking petroleum from natural seeps. See also 100 bce Energy.

Hippocrates founds a school of medicine on the Aegean island of Cos. His followers develop the Hippocratic Oath, still taken by physicians, and encourages separation of medicine from religion. This earns him the sobriquet "the Father of Medicine." Inspired by Empedocles' theory of four elements, the Hippocratic medical tradition eventually develops the theory of the four humors in the human body -- blood, phlegm, yellow bile, and black bile. An imbalance in the humors is thought to be the cause of illness.

Hippocrates writes the first clinical description of diphtheria.

Locks operated with keys are invented in Sparta (Greece).

Semilegendary Chinese artisan Lu Pan produces the first known kite. See also 1232 Communication.

500s BC · 400s BC · 300s BC
Decades of the 400s BC:
490s BC · 480s BC · 470s BC · 460s BC · 450s BC · 440s BC · 430s BC · 420s BC · 410s BC · 409–400 BC

400s BC may refer to:

• The period from 499 BC to 400 BC, almost synonymous with the 5th century BC
• 409–400 BC, rarely

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