During the last twenty-five years a number of authors have studied the influence of chemical substances on limb regeneration in amphibians. Examples of compounds which have been tested so far are: (1) the antimitotic agent, colchicine (Thornton, 1943); (2) the salt, beryllium nitrate (Thornton, 1949, 1950, 1951); (3) the carcinogens, dibenzanthracene and methylcholanthrene (Karczmar & Berg, 1952; Ruben & Balls, 1964); (4) the lathyrus factor, β- aminopropionitrile (Chang, Witschi & Ponseti, 1955); (5) the hormone, thyroxine (Hay, 1956); (6) atropine and other neuropharmacological drugs (Singer, Davis & Scheuing, 1960); (7) the metachromatic dye, toluidine blue (Csaba, Bierbauer & Törö, 1961); and (8) semicarbazide, an inhibitor of histamine formation (Deck & Shapiro, 1963). Most of these substances caused growth retardation as well as malformations of the limb regenerates.
A number of other investigators have studied the effects of chemicals on the ontogenetic development of the amphibian limb.