Webster's New World Medical Dictionary

nitrogen narcosis
A condition similar to intoxi-
cation with alcohol characterized by euphoria, loss
of balance and manual dexterity, disorientation, and
impaired reasoning. It can occur in scuba divers
below 30 meters (100 feet) who breathe com-
pressed air, because of the high nitrogen content of
air. Nitrogen narcosis is reversed as the gas pressure
decreases and the diver returns toward the surface.
nitrogenous base
A molecule that contains
nitrogen and has the chemical properties of a base.
The nitrogenous bases in DNA are adenine (A), gua-
nine (G), thymine (T), and cytosine (C). The
nitrogenous bases in RNA are the same, with one
exception: adenine (A), guanine (G), uracil (U),
and cytosine (C).
nitroglycerin
A medication used to dilate blood
vessels and improve blood flow. Nitroglycerin has a
rapid effect and is used to treat angina pectoris by
increasing blood flow to the heart. Nitroglycerin
tablets are taken sublingually (under the tongue).
Also known as nitro, NTG.
nitrosourea
One of a group of anticancer drugs
that can cross the blood–brain barrier.
nitrous oxide
A gas that can cause general anes-
thesia and that should be administered with other
anesthetic agents. Nitrous oxide is not used alone
today because the concentration of nitrous oxide
needed to produce anesthesia is close to the con-
centration that seriously lowers the blood oxygen
level, creating a hazardous hypoxic state. Nitrous
oxide is used sometimes as a recreational drug for
its euphoric effect. Also known as laughing gas and
nitrous.
nits
Lice eggs. Nits are hard to see, and they are
often confused with dandruff or hair-spray droplets.
Nits firmly attach to the hair shaft with a glue-like
substance. They are oval and range in color from
yellow to white. Nits take about a week to hatch. All
nits must be removed to prevent reinfestation with
lice. They can be removed with a special comb or
with the fingers. Topical preparations are available
that loosen their attachment to hair, making
removal easier. See also 
head lice.