by certain neurons, which damp down
the action of other nerve cells to keep the
brain’s activity in balance. In psychoana-
lysis, inhibition refers to the unconscious
restraint of instinctual impulses.
injectionIntroduction of a substance into
the body from a syringe via a needle. In-
jections may be intravenous (into a vein),
intramuscular (into a muscle), intrader-
mal (into the skin), intra-articular(into a
joint), or subcutaneous (under the skin).
injuryHarm to any part of the body. It
may arise from many causes, including
physical influences (for example, force,
heat, cold, electricity, vibration, and radi-
ation), chemical causes(for example,
poisons), bites, or oxygen deprivation.
ink-blot testAn outdated psychologi-
cal test in which the subject was asked
to interpret the appearance of a number
of ink blots. The most widely used exam-
ple was the Rorschach test.
inlay, dentalA filling of porcelain or
gold used to restore a badly decayed
tooth. An inlay may be needed for the
back teeth or to protect a weakened tooth.
inoculationThe act of introducing a
small quantity of a foreign substance
into the body, usually by injection, for
the purpose of stimulating the immune
systemto produce antibodies(protec-
tive proteins) against the substance.
Inoculation is usually done to protect
against future infection by particular
bacteria or viruses (see immunization).
inoperableA term applied to any con-
dition that cannot be alleviated or
cured by surgery, particularly cancers.
inorganicA term used to refer to any of
the large group of substances that do
not contain carbon and to a few simple
carbon compounds (for example, carbon
dioxideand carbon monoxide). Examples
of inorganic substances include table
salt (sodium chloride) and bicarbonate
of soda (sodium bicarbonate).
inpatient treatmentCare or therapy
in hospital following admission.
inquestAn official inquiry by a coroner
into a death that is of unknown cause or
is suspected of being unnatural.
insanityA term for serious mental dis-
order. The term has no technical meaning.
insect bitesPuncture wounds inflicted
by bloodsucking insects such as gnats,mosquitoes,fleas, and lice. Most bites
cause only temporary pain or itching,
but some people have severe skin reac-
tions. In the tropics and subtropics,
insect bites are potentially more serious
because certain biting species can trans-
mit disease (see insects and disease).
All insect bites provoke a skin reaction
to substances in the insect’s saliva or
faeces, which may be deposited at or
near the site of the bite. Reactions vary
from red pimples to painful swellings or
an intensely itching rash; some insects,
such as bees and wasps, have stings
(see insect stings) that can produce fatal
allergies. (See also lice; spider bites;
mites and disease; ticks and disease.)
insects and disease Relatively few in-
sect species cause disease directly in
humans. Some parasitize humans, living
under the skin or on the body surface (see
lice; chigoe; myiasis). The most trouble-
some insects are flies and biting insects.
Flies can carry disease organisms from
human or animal excrement via their feet
or legs and contaminate food or wounds.
A number of serious diseases are spread
by biting insects. These include malaria
and filariasis(transmitted by mosqui-
toes), sleeping sickness (tsetse flies),
leishmaniasis(sandflies), epidemic typhus
(lice), and plague(rat fleas). Mosquitoes,
sandflies, and ticks can also spread ill-
nesses such as yellow fever, dengue,
Lyme disease, and some types of viral
encephalitis. Organisms picked up when
an insect ingests blood from an infected
animal or person are able to survive or
multiply in the insect. Later, the organ-
isms are either injected into a new human
host via the insect’s saliva or deposited
in the faeces at or near the site of the bite.
Most insect-borne diseases are con-
fined to the tropics and subtropics,
although tick-borne Lyme disease occurs
in some parts of the UK. The avoidance
of insect-borne disease is largely a mat-
ter of keeping flies off food, discouraging
insect bites by the use of suitable cloth-
ing and insect repellents, and, in parts
of the world where malaria is present,
the use of mosquito nets and screens,
pesticides, and antimalarial tablets.
insect stingsReactions produced by the
sting of insects such as bees and wasps.INJECTION INSECT STINGSI