When I graduated as a Veterinary Surgeon some 36 years ago, the number of effective anti parasitic components available for clinical use were remarkably few. Many natural products were still in use (extract of male fern, arecoline, oil of chenopodium, kamala, nicotine, derris and the like) many difficult to formulate and to administer, some requiring overnight fasting before use and purgation after use. The compounds of remarkable promise at that time were phenothiazine for nematodes in farm animals, carbon tetrachloride for liver fluke in sheep and cattle, the sulpha durgs for coccidia and two wonder drugs for the arthropods, DDT and BHC.