In 1909, Ehrlich determined, after a series of laboratory experiments on animals inoculated with the syphilis germ (spirochaeta pallida), that a complex compound, with arsenic as its base, had the desired effect of destroying the parasite, in a dose not poisonous to the animal. This compound, first designated as "606," representing its number among his many laboratory experiments, he later named "salvarsan." With the assistance of his clinical friends, he soon demonstrated the action of his compound on man, and gave it freely to the world. Although it is now almost universally used, it has not proved to be the absolute cure that it was hoped it would be, as some of the spirochaetae seem to be hidden away where they are protected from the circulating poison,--to bring forth new progeny,--thus producing so-called recurrence. The possibility of the infection of innocent persons is always uppermost in the mind of the medical man, and should equally concern the layman. Contaminated articles and utensils, such as towels and common drinking-cups, have caused many infections. This danger is greater from syphilis than from gonorrhea, for the reason that the spirochaeta pallida is more virulent than the gonococcus. In our own fields, camps, and mines, it is common for men to drink from one jug or dipper. Infection almost surely follows if one of the crowd has a syphilitic sore on the lip. So intense is the activity of the spirochaeta pallida in the primary stage that it may be borne to innocent parties by unwashed clothes and utensils of any kind, that have been in recent contact with a primary syphilitic sore. A dentist's or a doctor's instruments, for instance, are extremely dangerous as infection carriers, if they are not thoroughly sterilized by boiling. The danger of infection in syphilis and gonorrhea depends largely upon the virulence of the individual infection. As some living tubercle bacilli may be harbored and thrown off with impunity, while others will destroy the strongest man, regardless of all treatment, so some spirochaetae or gonococci may be safely disposed of, while others are most deadly.