Webster's New World Medical Dictionary

melena
Stool or vomit that is stained black by
blood pigment or dark blood products.
melorheostosis
A rare bone condition that usu-
ally begins in childhood and is characterized by
thickening of the bones (sclerosis) of a limb. Pain
is frequent in the involved limb, and the affected
bone can have the appearance of dripping candle
wax on an X-ray.
membrane
A very thin layer of tissue that covers
a surface.
membrane attack complex
An abnormal acti-
vation of the complement (protein) portion of the
blood that forms a cascade reaction and brings
blood proteins together, binds them to the cell wall,
and then inserts them through the cell membrane.
Abbreviated MAC. MAC allows water, ions, and other
small molecules to move freely into and out of a
cell, and it quickly results in cell death.
membranous gingivitis, acute
See 
acute
membranous gingivitis.
membranous glomerulonephritis
A disease
affecting the glomerulus, the tiny structure in the
kidney composed of capillary blood vessels that is
actively involved in the filtration of the blood to form
urine. The main sign of the disease is marked pro-
teinuria. The majority of cases are primary, meaning
the cause is not known. The remaining cases are
secondary to conditions such as cancer, infection,
and drug side effects. Membranous glomeru-
lonephritis is a glomerular immune-complex dis-
ease, in which immune deposits form in the
glomerular basement membrane, causing a mem-
brane-like thickening. Also known as membranous
nephropathy.
memory
The ability to recollect information
about past events or knowledge, and/or the process
of doing so. Memory is often divided into short-term
(also known as working, or recent, memory) and
long-term memory: Short-term memory recovers
memories of recent events, and long-term memory
is concerned with the more distant past. Some med-
ical disorders, such as Alzheimer’s disease, damage
the cognitive systems that control memory. Usually,
long-term memory is retained and short-term mem-
ory is lost; conversely, memories may become jum-
bled, leading to mistakes in recognizing people or
places that should be familiar. See also 
memory,
anterograde; memory, long-term; memory, short-
term.