The author first called the attention of the meeting to the principal facts which he had established in the two memoirs read to the Society in the year 1836. 1st, Of these the most important are, that when acids cause a red colour, and alkalis a green or yellow, in a blue vegetable infusion, they act on different substances;—the acids on erythrogen, and the alkalis on xanthogen. 2dly, That the compound of alkalis and xanthogen is of a yellow colour, and that when a blue infusion is changed to green, it is owing to the gradual intermixture of the newly generated yellow with the original blue.