N-Diethylsulphanilamide: a reagent for the colorimetric estimation of thyroxine.

as 'thyroxine'. The methods have been reviewed by Harington (1933) and Salter (1940). On adapting the original butanol-extraction procedure of Leland & Foster (1932), as modified by Blau (1935), to artificially. iodinated proteins, Reineke, Turner, Kohler, Hoover & Beezley (1945) compared their results with those of biological assay in the guinea pig and were led to conclude that the chemical methodreliably accounted for the thyroxinepresent; the properties of any non-thyroxine component of the butanol layer would need to parallel closely those ofthyroxine itself. From an examination ofthyroidgland preparations from different species, Parkes (1946) concluded that a fairly close relationship exists between acid-insoluble iodine (and total iodine) and the biological activity as determined in the Xenop<u tadpole. On the other hand, Deanesly