The poison which had already been shown to be especially effective in killing germs like those of syphilis was arsenic. The problem was to get arsenic into such a combination with other chemical substances that it would lose its poisonous quality for man, but still be poisonous for the spirochete of syphilis. Ehrlich and Hata began to make chemical compounds of arsenic in the laboratory with chemical substances like the dyes. As the compounds grew more complex they were tested on animals and some of them found to have the qualities for which their inventors were searching. Some of them are even used at the present time in the treatment of certain diseases. The six hundred and sixth compound in this series, when tested on syphilitic animals, was found to be extraordinarily efficient in killing the germ of syphilis, even when used in quantities so small as not to injure the animal. Among other things, there could be no better example of the importance of animal experiment in medicine. If the cause of syphilis had not been known, and the disease not given to animals, the discovery of salvarsan might never have been made. After extensive experiments on syphilitic rabbits, which showed that the drug could be given safely in amounts large enough to cure the animal at a single dose, it was tried on man, two physicians, Drs. Hoppe and Wittneben, volunteering for the test. When it was found that the drug did them no harm, it was used on syphilitic patients for the first time. As soon as its remarkable effect on the disease in them was fully established, Ehrlich announced the discovery before the medical society of Magdeburg, and the results were published in one of the most important of the German medical journals. Ehrlich then sent out from his own laboratory several thousands of doses of the new drug to all the principal clinics and large hospitals of the world for an extended trial. It was not until the results of this trial became apparent that he permitted its manufacture on a commercial scale. There could scarcely be a more ideal way of introducing a new form of treatment than the one adopted by Ehrlich, or one better surrounded by all the safeguards that conservatism could suggest.