e part of the body.

Mesentery (Gr. mesos, middle, and enteron, the intestine). A duplicature
of the peritoneum covering the small _intestine_, which occupies the
_middle_ or center of the abdominal cavity.

Metabolism (Gr. metabole, change). The _changes_ taking place in cells,
whereby they become more complex and contain more force, or less complex
and contain less force. The former is constructive metabolism, or
_anabolism_; the latter, destructive metabolism, or _katabolism_.

Microbe (Gr. mikros, little, and bios, life). A microscopic organism,
particularly applied to bacteria.

Microscope (Gr. mikro#3CC;s, small, and skopeo, to look at). An optical
instrument which assists in the examination of minute objects.

Molar (Lat. _mola_, a mill). The name applied to the three back teeth at
each side of the jaw; the grinders, or mill-like teeth.

Molecule (dim. of Lat. _moles_, a mass). The smallest quantity into which
the mass of any substance can physically be divided. A molecule may be
chemically separated into two or more atoms.

Morphology (Gr. morphe, form, and logos, discourse). The study of the laws
of form or structure in living beings.

Motor (Lat. _moveo_, _motum_, to move). The name of the nerves which
conduct to the muscles the stimulus which causes them to contract.

Mucous Membrane. The thin layer of tissue which covers those internal
cavities or passages which communicate with the external air.

Mucus. The glairy fluid secreted by mucous membranes.

Myopia (Gr. myo, to shut, and o#x1F64;ps, the eye). A defect of vision
dependent upon an eyeball that is too long, rendering distant objects
indistinct; _near sight_.

Myosin (Gr. mos, muscle). Chief proteid substance of muscle.

Narcotic (Gr. narkao, to benumb). A medicine which, in poisonous doses,
produces stupor, convulsions, and sometimes death.

Nerve Cell. A minute round and ashen-gray cell found in the brain and
other nervous centers.

Nerve Fiber. An exceedingly slender thread of nervous tissue.

Nicotine. The poisonous and stupefying oil extracted from tobacco.

Nostril (Anglo-Saxon _nosu_, nose, and _thyrl_, a hole). One of the two
outer openings of the nose.

Nucleolus (dim. of _nucleus_). A little nucleus.

Nucleus (Lat. _nux_, a nut). A central part of any body, or that about
which matter is collected. In anatomy, a cell within a cell.

Nutrition (Lat. _nutrio_, to nourish). The processes by which the
nourishment of the bo