Dictionary.net

• A substance composed of a mixture of formaldehyde and gelatin, used for making capsules or coating pills, when it is desired to act especially on the intestinal mucous membrane; the substance dissolves in the intestinal juices but is insoluble in the stomach.

1920 - A practical medical dictionary.
By Stedman, Thomas Lathrop

• Made of gelatin hardened with formic aldehyd.

1916 - Appleton's medical dictionary
By Smith Ely Jelliffe