in susceptible people (p. 490).
Oxalates Oxalates are various salts of oxalic
acid, a waste product of plant metabolism
found in a number of foods, notably spinach,
chard, beets, amaranth, and rhubarb. The
sodium and potassium salts are soluble, while
the calcium salts are insoluble and form
crystals that irritate the mouth and digestive
system. Soluble oxalates can combine with
calcium in the human kidney to form painful
kidney stones. In very large doses — a few
grams — oxalic acid is corrosive and can be
fatal.
Bracken-Fern Toxins Bracken-fern toxins
cause several blood disorders and cancer in
animals that graze on this common fern
(Pteridium), which is sometimes collected in
the young “fiddlehead” stage for human
consumption. Ostrich ferns, Matteuccia
species, are thought to be a safer source of
fiddleheads, but there’s little solid