Recently Seidell (13) has described a method for the preparation of a relatively stable silver compound of the anti-neuritic substance. He discovered that fuller's earth has the property of absorbing from its solutions the physiologically active substance which exerts an anti-neuritic effect. In this way it can be separated from certain other substances with which it is associated. From the fuller's earth the vitamin is extracted by barium hydroxid. The barium is quickly removed from the resulting extract as sulphate and lead acetate is subsequently added as a precipitant. The excess of lead is removed as sulphid, and the filtrate from this precipitate is evaporated rapidly under diminished pressure to a small volume, when a white amorphous substance separates. This is found to be inactive and is, therefore, discarded. Evaporation is continued in a vacuum desiccator and several crops of the white substance are secured and removed. The solution, which possesses great anti-neuritic activity, is finally evaporated to a thick viscous mass which can be finally brought to dryness. The physiological activity of the dried residue is retained for many months.

When this material is dissolved in a small volume of water and treated with silver nitrate, there is formed a voluminous precipitate, which does not contain the anti-neuritic substance. This precipitate is removed. To the filtrate silver nitrate and ammonium hydroxid are added. These reagents form a second silver precipitate which contains the desired vitamin. The filtrate is practically free from it. This procedure appears to be a distinct step in advance in the purification of this most interesting principle.

McCollum and Kennedy (13) conducted experiments with pigeons designed to show the importance of fat-soluble A as a factor in the etiology of experimental beri-beri, and to determine whether definite evidence could be secured as to whether the growth essential water-soluble B, which had been demonstrated on rats, was identical with the substance, specific starvation for which leads to beri-beri in birds. Their data indicated that any extracts of natural foods which furnish water-soluble B in growth tests with rats likewise effected "cures" of beri-beri pigeons. They were able to demonstrate that fat-soluble A plays no role in the production of experimental beri-beri in pigeons. These authors also found that acetone, ethyl acetate and benzene can extract from wheat germ, rendered fat free by extraction with ether, the anti-neuritic substance. It is now known, however, that these solvents are extremely inefficient for this purpose, and that not more than traces of the active substance can be isolated by their use as solvents.