Although the question of the chemical nature of the hormones has been a subject of interest for nearly two decades, progress in this field has been exceedingly difficult because of the lack of endocrine preparations of sufficient purity for accurate chemical studies. Recent extensive investigation, however, has led to vastly improved methods of preparation and ultimately to the isolation in pure crystalline form of a number of the hormones. Thus these heretofore inaccessible substances have been brought within the scope of attack by the chemist. Indeed, at present several hormones have been prepared in crystalline form and the chemical structure and method of synthesis of two of these have been definitely established. Also a number of other hormones have been prepared in a highly purified although noncrystalline state, and some information regarding their chemical properties has been obtained.
The first hormone to be isolated in crystalline form was epinephrine (1901).
THE CHEMISTRY OF THE HORMONES. JAMA. 1935;104(13):1175–1176. doi:10.1001/jama.1935.02760130125012