Don't think; try.

Scientists
Edward Jenner
English physician born in 1749 who developed vaccination by proving that cowpox inoculation prevents smallpox. His method launched modern immunology and ultimately led to smallpox's eradication in 1980.
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Edward Jenner's Other Quotes
I shall endeavour still further to prosecute this inquiry, an inquiry I trust not merely speculative, but of sufficient moment to inspire the pleasing hope of its becoming essentially beneficial to mankind.
The deviation of man from the state in which he was originally placed by nature seems to have proved to him a prolific source of diseases.