In remembering dosage it is often advisable for the prescriber not to try to remember the dose of each preparation of a drug, but to remember the dose of the drug itself; then the dose of the preparations can be called to mind by the following rules:

The dose of the fluidextract is the same in minims as the dose of the drug in grains.

The dose in minims of the tincture is usually ten times the dose in grains of the drug.

The dose of the extract is usually one-fifth the dose of the drug. For example:

Nux Vomica-dose, 1 grain. Fluidextract of Nux Vomica-dose, 1 minim. Tincture of Nux Vomica-dose, 10 minims. Extract of Nux Vomica-dose, 1/5 grain.

This, of course, is approximate only, but in the largest percentage of cases it answers all requirements and is often a valuable aid to memory. Where the dose of the drug is large, as 30 to 60 grains, the rule as to the tincture will not often apply.

A rule can hardly be given for preparations as infusions, elixirs, etc., but the fluidextract, tincture, and extract are the preparations of common use.