Thiourea: A photographic fixative used also in the manufacture of resins. According to the Fourth Annual Report on Carcinogens (NTP 85-002, 1985), this substance may reasonably be anticipated to be a carcinogen (Merck Index, 9th ed). Many of its derivatives are ANTITHYROID AGENTS and/or FREE RADICAL SCAVENGERS.PhenylthioureaEthylenethiourea: A degradation product of ethylenebis(dithiocarbamate) fungicides. It has been found to be carcinogenic and to cause THYROID hyperplasia.Spermatocidal Agents: Chemical substances that are destructive to spermatozoa used as topically administered vaginal contraceptives.Urea: A compound formed in the liver from ammonia produced by the deamination of amino acids. It is the principal end product of protein catabolism and constitutes about one half of the total urinary solids.Thioamides: Organic compounds containing the radical -CSNH2.Potassium Iodide: An inorganic compound that is used as a source of iodine in thyrotoxic crisis and in the preparation of thyrotoxic patients for thyroidectomy. (From Dorland, 27th ed)2,2'-Dipyridyl: A reagent used for the determination of iron.Isothiuronium: An undecenyl THIOUREA which may have topical anti-inflammatory activity.Tachyphylaxis: Rapidly decreasing response to a drug or physiologically active agent after administration of a few doses. In immunology, it is the rapid immunization against the effect of toxic doses of an extract or serum by previous injection of small doses. (Dorland, 28th ed)Hydroxides: Inorganic compounds that contain the OH- group.Cinchona Alkaloids: Alkaloids extracted from various species of Cinchona.PhloretinHydroxyl Radical: The univalent radical OH. Hydroxyl radical is a potent oxidizing agent.Benzoic Acid: A fungistatic compound that is widely used as a food preservative. It is conjugated to GLYCINE in the liver and excreted as hippuric acid.Rodenticides: Substances used to destroy or inhibit the action of rats, mice, or other rodents.Molecular Structure: The location of the atoms, groups or ions relative to one another in a molecule, as well as the number, type and location of covalent bonds.Cyclization: Changing an open-chain hydrocarbon to a closed ring. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)Allantoin: A urea hydantoin that is found in URINE and PLANTS and is used in dermatological preparations.