disorders of the eye include Leber’s
optic atrophyand senile macular degen-
eration. Degenerative disorders of the
joints include osteoarthritis.
Some hardening of the arteries seems
to be a feature of aging. In some peo-
ple, degenerative changes in the muscle
coat of arteries are unusually severe
and calcium deposits may be seen on
X-rays(as in Monckeberg’s sclerosis, a
type of arteriosclerosis). Several degener-
ative disorders, such as the muscular
dystrophies, are now known to be genetic.
dehiscenceThe splitting open of a partly
healed wound.
dehydrationA condition in which a per-
son’s watercontent is at a dangerously
low level. Water accounts for about 60
per cent of a man’s weight and 50 per
cent of a woman’s. The total water (and
mineral salts and other substances dis-
solved in the body’s fluids) content must
be kept within fairly narrow limits for
healthy functioning of cells and tissues.
Dehydration occurs due to inadequate
intake of fluids or excessive fluid loss.
The latter may occur with severe or pro-
longed vomiting or diarrhoea or with
uncontrolled diabetes mellitus, diabetes
insipidus, and some types of kidney fail-
ure. Children are especially susceptible
to dehydration by diarrhoea.
Severe dehydration causes extreme
thirst, dry lips and tongue, an increase
in heart rate and breathing rate, dizzi-
ness, confusion, lethargy, and eventual
coma. The skin looks dry and loses its
elasticity. Any urine passed is small in
quantity and dark-coloured. If there is
also salt depletion, there may also be
headaches, cramps, and pallor.
Bottled mineral water can help main-
tain the intake of salts. For vomiting
and diarrhoea, rehydration therapyis
needed; salt and glucose rehydration
mixtures are available from chemists.
In severe cases of dehydration, fluids
are given intravenously. The water/salt
balance is carefully monitored by blood
tests and adjusted if necessary.
déjà vuFrench for “already seen”. A
sense of having already experienced an
event that is happening at the moment.
Frequent occurrence may sometimes be
a symptom of temporal lobe epilepsy.Delhi bellyAnother name for gastroen-
teritisand infective diarrhoea caused by
ingesting contaminated food or water.
delinquencyBehaviour in a young per-
son that would be considered a crime in
an adult. The term is often extended to
include noncriminal behaviour such as
drug abuse, playing truant, or running
away from home. Juvenile delinquency
probably results from a combination
of social, psychological, and biological
factors. Child guidance or family therapy
may be recommended. Persistent offen-
ders may be sent to special schools,
taken into care, or made wards of court.
deliriumA state of acute mental confu-
sion, commonly brought on by physical
illness. Symptoms vary according to
personality, environment, and the seve-
rity of illness. They may include failure
to understand events or remember what
has been happening, physical restless-
ness, mood swings, hallucinations, and
terrified panic. High fever and distur-
bances of body chemistry are commonly
present. Children and older people are
most susceptible to delirium, particularly
during infection, after surgery, or when
there is a pre-existing brain disturbance
such as dementia. Drugs, poisons, and
alcohol are common precipitants.
delirium tremensA state of confusion
accompanied by trembling and vivid hal-
lucinations. It usually arises in alcoholics
after withdrawal or abstinence from alco-
hol. Early symptoms include restlessness,
agitation, trembling, and sleeplessness.
The person may develop a rapid heart-
beat, fever, and dilation of the pupils.
Sweating, confusion, hallucinations, and
convulsions may also occur. Treatment
consists of rest, rehydration, and sedation.
Vitamin injections, particularly of thiamine
(see vitamin B complex), may be given.
deliveryThe expulsion or extraction of
a baby from the mother’s uterus. In
most cases, the baby lies lengthwise
in the uterus with its head facing down-
wards and is delivered head first
through the vaginal opening by a com-
bination of uterine contractions and
maternal effort (see childbirth). If the
baby is lying in an abnormal position
(see breech delivery; malpresentation), if
uterine contractions are weak, or if theDEHISCENCE DELIVERYD