Webster's New World Medical Dictionary

393
smallpox 
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another via infected saliva droplets as occurs during
face to face contact. Persons with smallpox are most
infectious during the first week of illness because
that is when the largest amount of virus is present in
saliva. However, some risk of transmission lasts
until all scabs have fallen off. Also known as variola.
smallpox vaccine
A vaccine that contains a live
virus called vaccinia that is used to prevent small-
pox. The vaccine does not contain the variola virus
that causes smallpox, but exposes the immune sys-
tem to proteins that look like the virus so that an
immune response occurs. Through the use of the
vaccine, smallpox was eliminated from causing
human infection in the world in 1977. Routine vac-
cination against smallpox ended in 1972. The level
of immunity among persons who were vaccinated
before 1972 is uncertain. In people exposed to
smallpox who are not immune to the disease, the
vaccine can lessen the severity of or even prevent
the illness if given within 4 days of exposure.
smear, Pap
See 
Pap test.
smell
The sense that provides information about
an object’s scent, often giving clues to the palatabil-
ity of food, the safety of air, and other matters. The
organs of smell are made up of patches of tissue
called the olfactory membranes that are each about
the size of a postage stamp. These membranes are
located in a pair of clefts just under the bridge of the
nose. Most air breathed in normally flows through
the nose, but only a small part reaches the olfactory
clefts—just enough to get a response to an odor.
When a person sniffs to detect a smell, air moves
faster through the nose, increasing the flow to the
olfactory clefts and carrying more odor to these sen-
sory organs.