248 
ON THE PREPARATIONS OF SENEKA. 
subject, comprising a history of its constituents, and particu- 
larly of its active principle, polygalic acid, which he describes 
as a white, inodorous, pulverulent substance, unalterable in the 
air, and capable of producing very energetic effects on the 
animal economy. Its acid character appears to be well estab- 
lished, as it reddens litmus and combines with bases to form 
salts, which are uncrystallizable, but its intensity is so slight that 
it is incapable of displacing carbonic and hydrosulphuric acids 
from their combinations. It is this principle which causes the 
decoction of seneka to redden litmus, and which gives it the 
tendency to froth by agitation. It is analogous in many of 
its properties to saponin, and in some respects to sarsaparillin. 
Whefi in a pulverulent form it is brought in contact with the 
nasal membrane, it produces sneezing and local inflammation 
of the part, and when swallowed causes a painful astrictive 
sensation in the throat. 
Polygalic acid in a free state dissolves but slowly in cold 
water, but with great readiness when assisted by heat ; never- 
theless cold water removes it completely from the powdered 
root, which may be due to its association with other principles, 
as in the cases of sarsaparillin, cantharidin, etc. Boiling alco- 
hol dissolves it largely, from which by cooling it precipitates 
in a pulverulent form, and this is true also of dilute alcohol. 
Perhaps those who have prepared a tincture of seneka with 
the intention of resorting to it as occasion might require for 
making the syrup, have noticed a light coloured precipitate to 
separate after standing some time. This is polygalic acid; and 
should not be removed, as it will redissolve by the heat requi- 
site in the evaporation of the alcohol. This principle, not- 
withstanding its acid nature, appears to be incompatible with 
but few substances, and according to M. Quevenne, it may be 
associated without impropriety with all ordinary salts, except 
subacetate of lead and protonitrate of mercury. M. Que- 
venne isolated polygalic acid by treating the root with cold 
water by displacement, precipitating the cold infusion with 
