Changes undergone by phenylarsenious acid and phenylarsonic acid in the animal body

been studied when given by intravenous injection.In agreement with theory, increasing polarity of the molecule results in diminished toxicity.Mercapto- succinate, acetylmercaptosuccinate, mercaptoadi- pate, dimercaptoadipate and glutathione cause no pathological symptoms in rabbits in dosage of up to 1 g./kg.3. Many ofthese thiols when given by intravenous injection were able to prolong the life of rabbits given 3 LD50 of lewisite.4. The most effective th rapeutic action was obtained with BAL-INTRAL, which prevented death in 100 % of the animals studied, even if not given until 6*5 hr. after administration of 3 LD50 of lewisite (which in untreated animals kills in 10 to 20 hr.).5., Details -are given of the preparation of mer- captosuccinic acid, dimercaptoadipic acid, glucothiose, BAL-INTRAV (BAL glucoside), and a number of other thiol acids.We are deeply indebted, both for assistance and encouragement, to many friends at Cambridge, Oxford, and at the Ministry of Supply.We particularly wish to thank Prof. G. R.