Harden and Zilva (16) and Voegtlin and White (17) have attempted to repeat the studies of Williams and Seidell purporting to show that adenin and α-hydroxy py-ridin can acquire anti-neuritic properties. In all their tests they found no evidence that these compounds exert any curative action on pigeons suffering from polyneuritis. McCollum and Koch (18) have attempted to induce growth in young rats on diets lacking only the anti-neuritic substance, but containing instead adenin, pilocarpin hydrochlorid or adrenalin. In no instance was there the slightest indication that the physiologically indispensable complex was supplied by any of these compounds.

McCollum and Simmonds (19) also tested thymus nucleic acid as a source of the anti-neuritic principle, but with negative results.