Originally published in 1947, this classic study by D. J. Finney was the first to examine and explain a branch of statistical method widely used in connection with the biological assay of insecticides, fungicides, drugs, vitamins, etc. It standardized the computations and terminology and made its use easier for a biologist without statistical expertise, whilst also outlining the underlying mathematical theory. Finney had made several important contributions to the method in the past, and his own results are also included. The book contains a foreword by the influential insecticidal chemist Dr F. Tattersfield.