Bma Illustrated Medical Dictionary

when 2 eggs are fertilized at the same
time. They each have a placenta and
may be of different sexes. Twins occur in
about 1 in 80 pregnancies. (See also
pregnancy, multiple.)
twins, conjoinedIdentical twinsphysi-
cally joined due to a failure to separate
during development from a single fertil-
ized egg. Also called Siamese twins.
twitchSee fasciculation; tic.
tympanic membraneThe medical term
for the eardrum.
tympanometryA type of hearing test
used to establish the cause of conduc-
tive deafness. During the test, a probe
that contains a tone generator, a micro-
phone, and an air pump is introduced
into the outer-ear canal. The air pres-
sure in the ear is varied and tones are
played into it. The tone pattern reflect-
ed from the eardrumand received by
the microphone sreveals whether the
eardrum is moving normally. The test is
particularly useful in children because it
does not rely on a response from the
person being tested.
tympanoplastyAn operation on the
ear to treat conductive deafness by
repairing a hole in the eardrum (see
myringoplasty) or by repositioning or
reconstructing diseased ossicles.
typhoid feverAn infectious disease
contracted by eating food or drinking
water contaminated with the bacterium
SALMONELLA TYPHI. Typhoid fever is
spread by drinking water contaminated

with sewage, by

flies carrying the

bacteria from fae-

ces to food, or by

infected people

handling food.

The 1st symptom,

severe headache,

occurs 7–14 days

after infection and

is followed by fever,

loss of appetite,

malaise, abdominal

tenderness, consti-

pation, and often

delirium. Diarrhoea

soon develops. In

the 2nd week of ill-

ness, pink spots

develop on the chest and abdomen,

and the liver and spleenenlarge. Diag-

nosis is confirmed by a blood test or by

obtaining a cultureof typhoid bacteria

from blood, faeces, or urine. Treatment

is with antibiotic drugs. In rare cases,

the bacterium continues to be excreted

after recovery has taken place.

typhusAny of a group of infectious dis-

eases with similar symptoms that are

caused by rickettsiaeand are spread by

insects or similar animals.

Except in some highland areas of

tropical Africa and South America, epi-

demic typhus is rare today. Endemic

typhus, also called murine typhus, is a

disease of rats that is occasionally

spread to humans by fleas; sporadic

cases occur in North and Central Amer-

ica. Scrub typhus is spread by mitesand

occurs in India and Southeast Asia.

The symptoms and complications of

all types of typhus are similar. Severe

headache, back and limb pain, cough-

ing, and constipation develop suddenly

and are followed by high fever, a

measles-like rash, confusion, and pros-

tration. Left untreated, the condition

may be fatal, especially in elderly or

debilitated people.

A diagnosis is made by blood tests,

and treatment is with antibiotic drugs

and supportive treatment.

typingA general term for procedures by

which blood or tissues are classified

(see blood groups;tissue-typing).

TWINS, CONJOINED TYPING

T

TWINS

Placenta Placenta

Uterus

Cervix

Shared

placenta

NONIDENTICAL TWINS IDENTICAL TWINS

Uterus

Cervix