One hundred years ago, German doctor Paul Ehrlich developed the first effective chemotheraopy drug, Specifically, he was trying to find a cure for syphilis:

Ehrlich and Japanese student Sahachiro Hata produced their 606th preparation of an arsenobenzene compound in 1907. Ehrlich watched on Aug 31 two years later, as Hata injected chemical No. 606 into a rabbit with syphilitic ulcers. The next day, no live spirochetes could be found on the animal's ulcers, and within three weeksm the ulcers were completely gone.

After testing the drug on mice, guinea pigs and many more rabbits, Ehrlich and Hata sent their miracle cure to the chemical firm Hoechst, which marketed it under the name Salvarsan. The drug became an almost instant success around the world, although many criticized Ehrlich for creating a chemical that might encourage promiscuity.

Source: Neatorama