year, but most disappear after the age
of 9 years. Port-wine stains seldom
fade, but laser treatment performed in
adulthood can make some of them fade.
birthpoolA pool of warm water in
which a woman can sit to help relieve
pain during labour.
birth rateA measurement of the num-
ber of births in a year in relation to
the population.
birthweightA baby’s weight at birth
that usually ranges from 2.5–4.5 kg.
Birthweight depends on a number of
factors, including the size and ethnic
origin of the parents. Babies who weigh
less than 2.5 kg at birth are classified as
being of low birthweight. Causes of low
birthweight include prematurity and
undernourishment in the uterus (for
example, because the mother had pre-
eclampsia). Abnormally high birthweight
is often due to unrecognized or poorly
controlled diabetes mellitusin the mother.
bisexualitySexual interest in members
of both sexes that may or may not in-
volve sexual activity.
bismuthA metal, salts of which are used
in tablets to treat peptic ulcerand in
suppositories and creams to treat haem-
orrhoids. Bismuth preparations taken
by mouth may colour the faeces black.
The tongue may darken and occasional
nausea and vomiting may occur.
bisphosphonate drugs Drugs used to
slow bone metabolism (for example in
Paget's disease)and to reduce the high
calcium levels in the blood associated
with destruction of bone by secondary
cancer growths. Bisphosphonates are
also used in the prevention or treat-
ment of osteoporosis.
biteSee occlusion.
bites, animalAny injury inflicted by
the mouthparts of an animal, from the
puncture wounds of bloodsucking in-
sects to the massive injuries caused by
shark or crocodile attacks. Teeth, espe-
cially those of carnivores, can inflict
severe and widespread mechanical inj-
ury. Severe injuries and lacerations to
major blood vessels can lead to severe
blood loss and physiological shock. Ser-
ious infection may occur due to bacteria
in the animal’s mouth; and tetanusis a
particular hazard. In countries whererabiesis present, any mammal may po-
tentially harbour the rabies virus and
transmit it via a bite. Medical advice
should be sought for all but minor inj-
uries or if there is a possibility of rabies.
Treatment usually includes cleaning and
examination of the wound. The wound
will usually be left open and dressed.
Preventive antibiotic drugtreatment and
an antitetanus injection may also be
given. Antirabies vaccine is given, with
immunoglobulin, if there is any possibil-
ity that the animal is infected with the
rabies virus. (See also bites,human
insect bites; snake bites; spider bites;
venomous bites and stings.)
bites, humanWounds caused by one
person biting another. Human bites
rarely cause serious tissue damage or
blood loss, but infection is likely, partic-
ularly if the bite is deep. There is a risk
of tetanus infection. Transmission of
hepatitis B, herpes simplex, and AIDSby
a bite is a theoretical hazard.
black deathThe medieval name for
bubonic plague,which killed 50 per cent
of its victims. One feature of the disease
is bleeding beneath the skin, causing
dark blue or black bruises, hence the
name ‘black death’.
black eyeThe bruised appearance of
the skin around the eye, usually follow-
ing an injury. The discoloration is due
to blood collecting under the skin.
blackheadA semi-solid, black-capped
plug of greasy material, also known as a
comedo, blocking the outlet of a seba-
ceous (oil-forming) gland in the skin.
Blackheads occur most commonly on
the face, chest, shoulders, and back and
are associated with increased seba-
ceous gland activity. They are one of the
features of most types of acne.
blackoutA common term for loss of
consciousness (see fainting).
black teethSee discoloured teeth.
blackwater feverAn occasional and
life-threatening complication of falci-
parum malaria (the most dangerous
form of malaria). Symptoms include
loss of consciousness, fever, and vomit-
ing, and very dark urine (due to pigment
from destroyed red blood cells being fil-
tered into the urine), which gives the
condition its name.BIRTHPOOL BLACKWATER FEVERB