Seidell93bhas found that the precipitate obtained by addition of ammoniacal silver nitrate to a purified vitamin extract made from yeast " activated " fuller's earth is highly antineuritic. This vitamin silver complex is amorphous and its conversion to a crystalline condition has not been effected, but several crystalline derivatives of the active constituent of the compound have been obtained, including the picrate, nitrate, and what appears to be the free base. Of these, the picrate does not give a constant melting point and yields picric acid by ether extraction. The nitrate melts with decomposition at 146°. The base is very slightly soluble in strong alcohol but so soluble in water that a viscous pellicle is usually obtained on slow evaporation of the aqueous solution.

Funk 94 at first believed that the antineuritic vitamin was a pyri-midine base analogous to uracil acid and thymine, and was probably a constituent of nucleic acid; a theory which was supported by Ved-der and Williams.95 It seems evident, however, from later work,96 that the substances isolated have in all cases been nitrogeneous bases contaminated by traces of vitamin, rather than the vitamin itself in a pure condition. Antineuritic properties have been attributed to a variety of compounds; nicotinic acid,97 adenine,98 betaine," allantoic100 pyrimidines,101 hydroxy pyrimidines,102 to certain purine and choline-like bases isolated from rice polishings;103 to quinine and cinchonine,104 and to thyroxin, desiccated thyroid gland, pilocarpine hydrochloride, and tethlin,105 but in many cases when these substances are prepared in sufficiently pure condition they have proved to be inactive,106 and in no case has the vitamin been satisfactorily identified with a known substance. The work of Williams along this line seemed very promising, but unfortunately other workers have been unable to confirm his results.

93b Seidell, Public Health Reports, April 1, 1921; Science, Aug. 26, 1921, 177.

94 Funk, J. Physiol. 45, 75, 1912.

95 Vedder and Williams, Phil. J. Sci. B8, 175, 1913.

96 Dmmmond and Funk, Bioch. J. 1914, 8, 598; Barger, "The Simple Natural Bases," [Longmans] 1914, 112.

97 Funk, J. Physiol. 1913, 46, 177.

98 Williams and Seidell, J. Biol. Chem. 1916, 26, 431.

99 Funk, J. Physiol. 45, 489, 1912-13.

100 punk, Ibid.

101 Funk, J. Physiol. 45, 489, 1912-13; Williams, J. Biol. Chem. 39, 504, 1917.

102 Williams, J. Biol. Chem. 99, 504, 1917.

103 Vedder and Williams, Phil. J. Sci. 8B, 175, 1913.

Assuming from the properties of the active extracts that the curative substance was an hydroxy-pyrimidine, Williams107 prepared a series of pyrimidine derivatives and tested the therapeutic action of each on polyneuritic pigeons. The series included nicotinic, cin-chomeric, quinolinic, 6-hydroxy-nicotinic, and citrazinic acids, a-hydroxypyridine glutazine, 2, 3, 4-trihydroxypyridine, and its anhydride, 2, 3, 4-trihydroxypyridine, and tetrahydroxypyridine, of which only a-hydroxy-, 2, 4, 6-, and 2, 3, 4-trihydroxypyridine showed any curative effect. As it was noticed that preparations which were active when, fresh deteriorated rapidly on keeping,108 Williams suspected isomerization. He was able to prepare two isomeric crystalline forms of hydroxy-pyridine, needles and granules, which are isomeric and can be converted into one another, the stability of each form being determined by temperature, solvent and other conditions. Only the needle form shows curative power. On standing at room temperature the needles gradually become transformed into granules, with corresponding loss of curative power.

He concluded that the curative form is a pseudo-betaine and that more or less conformity to the betaine type in structure or energy conditions is an essential characteristic of antineuritic vitamins, and suggested that the curative properties of Funk's vitamin fractions of yeast and rice may have been due in part to a corresponding isomeric form of nicotinic acid or a polymer or simple derivative of it.108a.

Williams and Seidell,109 in their second paper on the subject, give expression to the following hypothesis: The vitamins contain one or more groups of atoms constituting nuclei in which the physiological properties are resident. In a free state these nuclei possess the vitamin activity but under ordinary conditions are spontaneously transformed into isomers which do not possess the antineuritic power. The complementary substances or substituent groups with which these nuclei are more or less firmly combined in nature exert a stabilizing and perhaps otherwise favorable influence on the curative nucleus, but do not in themselves possess the vitamin type of physiological potency. Accordingly it is believed that while partial cleavage of vitamins may result only in a modification of their physiological properties, by certain means disruption may go so far as to effect a complete separation of "nucleus" and "stabilizer" and, if it does so, will be followed by loss of curative power due to isomerization.

The basis for the assumption that an isomerization constitutes the final and physiologically most significant step in the inactivation of a vitamin is found in studies of synthetic antineuritic products, and is supported by evidence of the existence of such an isomerism in the crystalline antineuritic substance obtainable from brewers' yeast. Williams holds that natural antineuritic substances, from the same or different raw materials may differ both in respect to the ease with which the stabilizing groups or substances are detached and to the rapidity with which the resulting free curative nucleus is transformed into a non-curative isomer. The acceptance of this hypothesis does not predicate anything with regard to the number or identity of the curative nuclei in the various antineuritic feeding stuffs nor does it negative the possibility of an actual disruption and decomposition of the vitamin molecules as a contributory cause of their stability. Harden and Zilva110 question the view that hydroxypyridine cures or improves the condition of polyneuritic birds. They confirm the existence of two isomeric forms of this compound, but failed to observe any curative action of either form.

104 Cooper, Bioch. J. 7, 268, 1913.

105 Dutchcr, J. Biol. Chem. 39, 63, 1919.

106 Drummond and Punk, 1. c; Voegtlin and White, J. Pharm. Exp. Ther. 1316, 9, 165; Harden and Zilva, Bioch. J., 1917, 11, 172; Steenbock, Proc. Am. Physiol. 800. Am. J. Physiol. 4a, 610.

107 Williams, R. R., J. Biol. Chem. 25, 437, 1916. 108 Williams, R. R, J. Biol. Chem. 29, 495, 1917.

108a R. R. Williams believes that vitamin B eventually will be found to be a cyclic nitrogen compound with an oxygen substitution in the ring and capable of existence in a betaine configuration. (J. Ind. Eng. Chem. 1921, 1108).

109 J. Biol. Chem. 26, 431, 1916.

110 Harden and Zilva, Bioch. J.,11, 173, 1017.