effort, we can, to a certain extent, restrain or control the motion.

STRUCTURE OF THE MUSCLES.--If we take a piece of lean beef and wash out
the red color, we can easily detect the fine fibers of which the meat is
composed. In boiling corned beef for the table, the fibers often separate,
owing to the dissolving of the delicate tissue which bound them together.
By means of the microscope, we find that these fibers are made up of
minute filaments (_fibrils_), and that each fibril is composed of a
row of small cells arranged like a string of beads. This gives the muscles
a peculiar striped (striated) appearance. [Footnote: The involuntary
muscles consist generally of smooth, fibrous tissue, and form sheets or
membranes in the walls of hollow organs. By their contraction they change
the size of cavities which they inclose. Some functions, however, like the
action of the heart, or the movements of deglutition (swallowing), require
the rapid, vigorous contraction, characteristic of the voluntary muscular
tissue--FLINT.] (See p. 276.) The cells are filled with a fluid or
semifluid mass of living (protoplasmic) matter.

FIG. 15.

[Illustration: _Microscopic view of a Muscle, showing, at one end, the
fibrille; and, at the other, the disks, or cells, of the fiber._]

The binding of so many threads into one bundle [Footnote: We shall learn
hereafter how these fibers are firmly tied together by a mesh of fine
connective tissue which dissolves in boiling, as just described] confers
great strength, according to a mechanical principle that we see
exemplified in suspension bridges, where the weight is sustained, not by
bars of iron, but by small wires twisted into massive ropes.