The treatment of amphibian and chick embryos during the early stages of development with small concentrations of benzimidazole, and some of its derivatives, results in the formation of abnormal embryos (Liedke, Engleman, & Graff, 1954; Waddington, Feldman, & Perry, 1955a; Billett & Perry, 1957 a, b). The gross effects produced by these substances are of a fairly general kind. Abnormal gastrulation, decomposition of neurulae, and microcephaly are produced in Amphibia. Rather less well-defined abnormalities, involving the head, neural tube, and somites, are seen in the chick.
The way in which these abnormalities are produced is not known. The idea that benzimidazole acts simply as a purine anti-metabolite is not well founded (Slonimski, 1954). The work of Tamm and his colleagues (Tamm, Folkers, Shunk, & Horsfall, 1953; Tamm, 1958) has shown that benzimidazole and certain of its derivatives inhibit the growth of some viruses.