Fig. 174. Moulds used in making Litmus.
a. The lower or cell-piece.
b. The upper piece.
This image is from Lacmus in Pereira's Elements of Materia Medica and Therapeutics, 1854.
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Henriette's herbal is one of the oldest and largest herbal medicine sites on the net. It's been online since 1995, and is run by Henriette Kress, a herbalist in Helsinki, Finland.