Acting on this clue, Williams (11) prepared certain α-hydroxy pyridins and tested them for anti-neuritic properties by injecting them into polyneuritic pigeons. A number of cures were effected. On keeping, these preparations lost within a few days all curative power. From these findings Williams drew the deduction that the substances underwent a spontaneous change from an unstable to a stable form and that the latter was inactive. By treatment of inactive preparations with alcoholic sodium hy-droxid he found it possible to transform them into the physiologically active condition. From the method of manipulation and treatment, he was justified in assuming that he had in the active preparation the enol form of the substance. None of Williams' synthetic preparations had anything like the activity or certainty of action that is seen in extracts of certain natural foods. He was led to surmise that the pathological condition of polyneuritis is not due to a deficiency of a substance per se, but to a lack of a certain type of potential energy which only certain substances can supply. In other words, he suggested that it was the potentiality of isomeric change, in the substance administered, which produced the physiological effect of restoring function to a paralyzed bird. To this isomeric change, Williams attributed the instability of the vitamins of natural foods. He did not draw the conclusion that the anti-neuritic vitamin is a hydroxy-pyridin, but pointed out that the same type of isomerism is possible in bodies of entirely unrelated natures such as pyrimidins, purins and other heterocyclic compounds.