October 31:
(1) (1831) Italian neurologist, physiologist, and anthropologist Paolo Mantegazza is born. He is most famously known for his experiments with cocaine and its effects on the human psyche.
(2) (1835) German chemist Adolf von Baeyer is born. He is known for synthesizing indigo and for his experiments on uric acid derivatives.
(3) (2011) On this day in 2011, the human global population hits seven billion. This day is now recognized as Seven Billion Day by the UN.
