ON DIGITALIS PURPUREA. 
209 
consideration of the tinctures of digitalis at present in use, re- 
serving other preparations for some future communication. 
The alcoholic tinctures of the pharmacopoeial processes vary 
in the strength of the alcohol. In the British isles, however, 
that made use of is proof spirit. Let us, therefore, inquire 
how far this menstruum is effectual, and whether the previous 
treatment of the plant occasions important changes in its 
powers. The first step towards forming the tincture is to dry 
the leaves, and this process is differently directed by the 
colleges. We have no experiments on record of the results 
of various methods of drying; we are, therefore, left to draw 
our conclusions from analogy. 
We know that in the case of some active medicines, drying, 
especially by heat, effects considerable changes. White 
briony, a highly acrid and poisonous substance when recent, 
becomes comparatively mild by drying; and I have found that 
its chemical constitution is so far altered, that although an in- 
fusion of the fresh root affords a precipitate with tincture of 
galls, the infusion of the root, dried, even without heat, does 
not. The recent root of Arum maculatum, if chewed, 
will blister the mouth, and if rubbed on the hands will exco- 
riate them; yet, when dried, it is not only innoxious, but is 
used as an article of food. 
The bitter cassava root " when raw, is a most fatal poison 
to man and beast; but prepared by fire (baking) it is very 
safe, and the natural bread of the Indians and several Euro- 
peans."* 
Garlic is highly acrimonious; by drying it loses this quality, 
the same observation applies nearly to the whole onion tribe. 
The acrid seeds of the Palma Christi become mild by dry- 
ing. Mezereon bark, if applied to the skin, while recent, 
raises a blister; but by drying, it loses this quality. 
Many other instances might be adduced; it is true that they 
prove nothing in the case of digitalis, and they may be op- 
posed by the known efficacy of digitalis powder when well pre- 
*Stedman's Narrative, p. 382. 
vol. v. — no. in. 27 
