temperature of the eardrum. Both ver-
sions give an almost instant reading.
There are also disposable skin ther-
mometers that employ heat-sensitive
chemicals, which change colour at
specific temperatures. These are not as
reliable, however. Clinical thermom-
eters may be calibrated in degrees
Celsius (centigrade), degrees Fahren-
heit, or sometimes both.
thiabendazoleSee tiabendazole.
thiamineSee vitamin B complex.
thiazidesA type of diuretic drug.
thiopentalA barbiturate drugthat is
widely used as a general anaesthetic
(see anaesthesia, general). Thiopental is
given by intravenous injection.
thioridazineAn antipsychotic drug used
to treat schizophrenia. It is now used only
under specialist supervision because of
potentially serious side effects.
thirstThe desire to drink. Thirst is one
means by which the amount of water in
the body is controlled (the other is the
volume of urine excreted).
Thirst is stimulated by an increased
concentration of salt, sugar, or certain
other substances in the blood. As the
blood passes through the hypothalamus
in the brain, special nerve receptors are
stimulated, inducing the sensation of
thirst. Thirst is also stimulated if blood
volume decreases as a result of sweating,
vomiting, diarrhoea, severe bleeding, or
extensive burns. Thirst may also be
caused by a dry mouth.
thirst, excessiveA strong and persis-
tent need to drink, most commonly due
to dehydration. Other causes include
untreated diabetes mellitusand diabetes
insipidus, kidney failure, treatment with
phenothiazine drugs, and severe blood
loss. Abnormal thirst may also be due
to a psychological condition known as
psychogenic polydipsia.
thoracic outlet syndromeA condition
in which pressure on the brachial plexus
causes pain in the arms and shoulders,
pins-and-needles sensation in the fin-
gers, and weakness of grip and other
hand movements. Severe symptoms are
usually caused by a cervical rib. Thoracic
outlet syndrome may also be caused by
drooping of the shoulders, an enlarged
scalenus muscle in the neck, or a tumour.
The condition is made worse by lifting
and carrying heavy loads or by increases
in body weight.
Treatment of thoracic outlet syndrome
usually consists of exercises to improve
posture, sometimes together with non-
steroidal anti-inflammatory drugs and
muscle-relaxant drugs. Severe cases
may be treated by surgical removal of
the 1st rib.
thoracic surgeryA surgical speciality
concerned with operations on organs
within the chest cavity. Sometimes, tho-
racic surgery is combined with heart
surgery, in which case it is known as
cardiothoracic surgery.
thoracotomyAn operation in which
the chest is opened to provide access to
organs in the chest cavity.
There are 2 types of thoracotomy:
lateral and anterior. In a lateral thora-
cotomy the chest is opened between 2
ribs to provide access to the lungs,
major blood vessels, and the oeso-
phagus. In an anterior thoracotomy, an
incision down the sternum (breast-
bone) provides access to the heartand
the coronary arteries.
thoraxThe medical name for the chest.
The thorax extends from the base of the
neck to the diaphragm muscle.
thoughtThe mental activity that enables
humans to reason, form judgments, and
solve problems. The essential features
of thought include the substitution of
symbols (in the form of words, numbers,
or images) for objects, the formation of
symbols into ideas, and the arrangement
of ideas into a certain order in the mind.
(See also thought disorders.)
thought disordersAbnormalities in
the structure or content of thought,as
reflected in a person’s speech, writing,
or behaviour. Schizophreniacauses sev-
eral thought disorders, including loss of
logical connections between associa-
tions, the invention of new words (see
neologisms), thought blocking (sudden
interruption in the train of thought), the
feeling that thoughts are being inserted
into or withdrawn from the mind, and
auditory hallucinations.
Incoherent thoughts occur in all types
of confusion, including dementiaand
delirium. Rapidly jumping from one ideaTHIABENDAZOLE THOUGHT DISORDERS
T