166 ^ Treatise on 
flood to cool, will thicken into a mucilaginous 
Mafs, like Glue •, which by a further Evaporation 
becomes a folid Extradl. This may be moiftened 
with fome aromatick eflential Oil, and put by as 
the true and much the beft Extract of Colocynth, 
being a gentle Cathartick from gr. iv. to xv. 
Upon the whole we may conclude, that the Parts 
in this Drug, to which its purgative Virtue is ow- 
ing, are of two Kinds (viz.) oily Parts, and acrid 
Saline. And thefe Principles are found, not only 
in Colocynth, but in other ftrohg Catharticks, fuch 
as Tobacco, Hellebore, &V. thefe Subftances 
abounding with an Oil, which is extremely acrid, 
and produces the mofl violent Irritation of the 
Nerves. Thus, for Inftance, the leafl Drop of the 
Oil of Tobacco, being let fall into a Wound in an 
Animal, Convulfions of the whole Body immedi- 
ately follow, and the Animal very foon expires. 
Neither is this acrid Oil, which irritates the Nerves, 
contained only in the flronger Catharticks, but a 
great Number of bitter Vegetables are alfo found 
to be injurious to the Nerves j in fome Animals, 
and in Birds efpecially, bringing on Convulfions and 
Death, as appears from the Obfervations of M^pfler^ 
in his Treatife De Cicutd Aquatica: And the Bitter- 
nefs of thefe Compounds depends chiefly upon an 
acrid Oil, as is evident from a Refolution of them 
into their Principles. 
Now to thefe oily Parts is owing, in a fpecial 
Manner, the Adtion of the rougher Purgatives *, 
for by thefe the nervous Membranes of the Intef- 
tines, and the Nerves of the other Bowels, are 
forcibly vellicated and fhook ^ whence all the Glands 
of thofe Parts, being flrongly compreffed, fqueeze 
out their Contents, and pufh them forward to the 
Inteflines. To this End likewife, the other Prin- 
ciple which is found in purging Medicines, is con- 
ducive 
