Speed Reads

Old time medicine

This ancient arthropod blood has saved your life

This ancient arthropod blood has saved your life

Pop quiz: what is bright blue, has barely changed in the past 450 million years, and sells for $15,000 per liter? Answer: horseshoe crab blood, which is used to make sure injected drugs aren't contaminated with bacteria. Hank Green explains below. So cool! --Ryan Cooper