A search of the literature has revealed no carefully controlled work showing that any organic mercurial compound can be relied on to kill the spores of anaerobic bacteria. Nevertheless, claims have been made that these compounds can be depended on for the sterilization of instruments, and vast quantities of them are sold to physicians and dentists for that purpose. Mercury in its various forms has been used in medicine since the time of the early alchemists, but it remained for Robert Koch1to popularize its use as an antiseptic. Immediately after his famous string experiments with anthrax spores the medical world believed that it had in its hands an all powerful germicide which would destroy any disease-producing organism, because apparently Koch had shown that very great dilutions of mercury bichloride would kill the spores of the most resistant organisms. Only a few years after this idea had become thoroughly