Digitalis leaf preparations from different localities show great differences in pharmacologic strength. This variation in pharmacologic efficiency is due to the fact that there are a number of factors, variations in which will modify the amount of the active substances contained in the leaves. Among these factors are the soil, the gathering season, the methods of collecting and drying the leaves and the methods used in preserving the dried product. Carefully trained apothecaries may render the conditions fairly constant for one locality, but even then the leaves themselves are found to vary greatly from year to year. This variation in strength will of course be found also in the Galenic preparations made from the dried leaves.
In 1902 Fraenkel1 studied the strength of digitalis and strophanthus preparations obtainable in Heidelberg and the surrounding towns, that is, the leaf and seed preparations of practically one section. His material
BOOS WF, NEWBURGH LH, MARX HK. THE USE OF DIGIPURATUM IN HEART-DISEASE. Arch Intern Med (Chic). 1911;VII(4):551-560. doi:10.1001/archinte.1911.00060040112008