It has long been known that in certain circumstances the dye-stuff indigo, or substances very nearly related to it, may appear as products of animal metabolism, and this fact has not failed to attract attention from physiologists, chemists and medical men. Indigo, in fact, possesses a “fatal gift of beauty,” which has always made it a focus of interest. Of no substance is the history easier to trace. In the earliest times it was obtained from the plant Isatis tinctoria, and served as dye and pigment under the name of woad, being no doubt a striking feature at meetings of the wild Silures in this locality some 2,000 years ago. More recently, during the past half century, the problem of the production of synthetic indigo has absorbed enormous sums of money and the energies of an army of chemists, and the successful competition which it now wages with the vegetable product forms one of the best instances of the return eventually obtained by those who cast their bread upon the waters, financing research in the hope of a return which they cannot definitely foresee.