text: In 1906 Ehrlich developed a new derivative of arsenic compound, which he code-named Compound 606 (the number representing the series of all his tested compounds). The compound was effective against malaria infection in experimental animals. In 1905, Fritz Schaudinn and Erich Hoffmann identified a spirochaete bacterium (Treponema pallidum) as the causative organism of syphilis. With this new knowledge, Ehrlich tested Compound 606 (chemically arsphenamine) on a syphilis-infected rabbit. He did not recognise its effectiveness. Sahachiro Hata went over Ehrlich's work and found on 31 August 1909 that the rabbit, which had been injected with Salvarsan 606, was cured using only a single dose, the rabbit showing no adverse effect.
  The normal treatment procedure of syphilis at the time involved two to four years routine injection with mercury. Ehrlich, after receiving this information, performed experiments on human patients with the same success. After convincing clinical trials, the compound number 606 was given the trade name "Salvarsan", a portmanteau for "saving arsenic". Salvarsan was commercially introduced in 1910, and in 1913, a less toxic form, "Neosalvarsan" (Compound 914), was released in the market. These drugs became the principal treatments of syphilis until the arrival of penicillin and other novel antibiotics towards the middle of the 20th century. 
  Ehrlich created the concept of magic bullet based on the development of arsphenamine and introduced the English phrase "magic bullet" in The Harben Lectures for 1907 of the Royal Institute of Public Health at London. However, he had used the German word Zauberkugel in his earlier works on the side-chain theory. The magic bullet became the foundation of modern pharmaceutical research.