prepared a thesis for his doctorate on the embryonic
development of the cuttle-fish Sepiola and the crus-
tacean Nelalia.
In 1882, in a private laboratory he set up, he dis-
covered the phenomenon of phagocytosis. In 1888 he
went to Paris, where Louis Pasteur gave him a labora-
tory and an appointment in the Pasteur Institute, where
he remained for the rest of his life.
Apart from his work on phagocytosis, Mechnikov
published many papers on the embryology of inverte-
brates. These included work on the embryology of
insects, published in 1866, and, in 1886, his studies of
the embryology of medusae. At the Pasteur Institute in
Paris, Mechnikov was engaged in work associated
with the establishment of his theory of cellular immu-
nity. He published several papers and two volumes on
the comparative pathology of inflammation (1892),
and in 1901 he published a treatise entitled L’Immu-
nité dans les Maladies Infectieuses(Immunity in infec-
tious diseases). In 1908 he was awarded, together with
Paul EHRLICH, the Nobel Prize in physiology or
medicine.
He later proved that syphilis can be transmitted
to monkeys and took up the study of the flora (lactic-
acid-producing bacteria) of the human intestine
and developed a theory that senility is due to poison-
ing of the body by the products of certain of these
bacteria.
Mechnikov received many distinctions, among
which were the honorary D.Sc. of the University of
Cambridge, the Copley Medal of the Royal Society
of which he was a foreign member, the honorary
memberships of the Academy of Medicine in Paris
and the Academies of Sciences and of Medicine in St.
Petersburg. In addition, he was a corresponding
member of several other societies and a foreign mem-
ber of the Swedish Medical Society. He died on July
16, 1916.
mediator modulator(immune modulator; messenger)
An object or substance by which something is mediat-
ed, such as:
- A structure of the nervous system that transmits
impulses eliciting a specific response. - A chemical substance (transmitter substance) that
induces activity in an excitable tissue, such as nerve
or muscle (e.g., hormones).- Asubstance released from cells as the result of an
antigen-antibody interaction or by the action of anti-
gen with a sensitized lymphocyte (e.g., cytokine).
- Asubstance released from cells as the result of an
Concerning mediators of immediate hypersensitivi-
ty, the most important include histamine, leukotriene
(e.g., SRS-A), ECF-A, PAF, and serotonin. There also
exist three classes of lipid mediators that are synthe-
sized by activated mast cells through reactions initiated
by the actions of phospholipase A2. These are
prostaglandins, leukotrienes, and platelet-activating
factors (PAF).medicinal chemistry A chemistry-based discipline,
also involving aspects of biological, medical, and phar-
maceutical sciences. It is concerned with the invention,
discovery, design, identification, and preparation of
biologically active compounds; the study of their
METABOLISM; the interpretation of their mode of action
at the molecular level; and the construction of STRUC-
TURE-ACTIVITY RELATIONSHIPS.medulla oblongata One part of the brain stem,
along with the midbrain, pons, and reticular formation;
connects the brain to the spinal cord through the fora-
men magnum. Nerve tissue that deals with vital func-
tions in respiration, circulation (heart rate, blood flow),
and vasomotor; controls reflexes such as coughing,
sneezing, swallowing, vomiting, and gagging.medusa One of two basic life cycles of Cnidaria (i.e.,
hydra, jellyfish, anemones, and corals), the other being
polyps. The medusa form is a free-swimming, floating,
umbrellalike, flat, mouth-down version. Polyps’ forms
are sessile. Body parts on both forms are similar. Most
medusa have separate sexes. The eggs are fertilized
after they are shed into the water and usually grow into
polyp form that, in a form of asexual reproduction,
may break into multiple medusas.megapascal(MPa) A unit of pressure. 1 MPa =
1,000,000 Pa (pascal). 1 megapascal (MPa) = 10 bars.
A value of 1 bar is approximately equal to one atmo-
sphere of pressure.214 mediator modulator