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(A) Deep anesthesia of a fish with tricaine methane sulfonate (MS222), achieved by immersion in aqueous solution with the drug. Drug is taken up across the gills during respiration and, to a lesser extent, across the skin. Photo courtesy of Gerry Johnson. (B) Amphibians may be similarly dosed in aqueous chambers as in the Xenopus laevis depicted; however, substance uptake is solely through trancutaneous absortion.
