placenta praevia Implantation of the
in the lower part of the uterus,
near or over the cervix. Placenta praevia
occurs in about 1
in 200 pregnancies. It
varies in severity from marginal placen-
ta praevia, when the placenta reaches
the edge of the cervical opening, to
complete placental praevia, when the
entire opening of the cervix is covered.
Mild placenta praevia may have no
adverse effect. More severe cases often
cause painless vaginal bleeding in late
pregnancy. If the bleeding is slight and
the pregnancy still has several weeks to
run, bed rest in hospital may be all that
is necessary. The baby will probably be
38th week. If the bleeding is heavy or if
the pregnancy is near term, an immedi-
ate delivery is carried out.
placenta, tumours of See
nom a; hydatidiform mole.
plague A serious infectious disease that
is caused by the bacterium
y e r s in ia
p e s t i s .
It mainly affects rodents but can
be transmitted to humans by flea bites.
There are 2 main types: bubonic and
pneumonic plague. Bubonic plague is
characterized by swollen lymph glands
(called "buboes"). Symptoms usually
start 2-5 days after infection, with fever,
shivering, and severe headache. Soon,
the smooth, red, intensely painful bu-
boes appear, usually in the groin. There
may be bleeding into the skin around
the buboes, causing dark patches.
Pneumonic plague affects the lungs and
can spread from person to person in in-
fected droplets expelled during coughing.
Symptoms are severe coughing that pro-
laboured breathing. Without early treat-
ment, death is almost inevitable.
A sample of fluid from a bubo, or a
sputum sample, is taken to confirm the
diagnosis. Possible treatments include
of the sole of
plantar wart See
plants, poisonous Several species of
plant, including foxglove, holly, deadly
nightshade, and laburnum, are poison-
ous. Nettles, hogweed, poison ivy, and
primula cause skin reactions, including
rash and itching, on contact. Young chil-
dren are the most commonly affected.
Symptoms of poisoning vary according
to the plant but may include abdominal
pain, vomiting, flushing, breathing diffi-
urgent medical advice. Skin reactions
can be treated by application of alcohol
or calamine lotion;
may be prescribed for severe reactions.
Poisoning usually requires gastric
Fatal poisoning is rare. (See also
plaque The term given to an area of
The plaques are symp-
tomless until they are large enough to
reduce blood flow or until the surface of
a plaque is disturbed, causing
Plaques in coronary arteries cause
coronary artery disease.
plaque, dental A rough, sticky coating
on the teeth consisting of saliva, bacte-
ria, and food debris. It is the chief cause
of tooth decay (see
gingivitis, and forms the basis of a hard
in plaque, particu-
str epto c o ccu s m u ta n s,
sugar in the remains of carbohydrate
food that sticks to the mucus, creating
an acid that can erode tooth enamel,
plasma The fluid part of
remains if the blood cells are removed,
plasmapheresis A procedure for the
removal or reduction in concentration
of unwanted substances in the blood;