On Food and Cooking

exercise bulk up the muscle fibers, they also
bulk up and toughen the connective tissue.
Connective tissue includes some living
cells, but consists mainly of molecules that
the cells secrete into the large spaces between
them. The most important of these molecules
for the cook are the protein filaments that run
throughout the tissue and reinforce it. One, a
protein called elastin for its stretchiness, is
the main component of blood vessel walls and
ligaments, and is especially tough; its cross-
links cannot be broken by the heat of cooking.
Fortunately there isn’t much of it in most
muscle tissue.
The major connective-tissue filament is
the protein called collagen, which makes up
about a third of all the protein in the animal
body, and is concentrated in skin, tendons, and
bones. The name comes from the Greek for
“glue producing,” because when it’s heated in
water, solid, tough collagen partly dissolves
into sticky gelatin (p. 597). So unlike the