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GLOSSARY 299

Periportal Near the portal vein and branches of this vein. a fixative for cell and parasite preparations for microscopic
Peristalsis Refers to the symmetrical contraction of smooth examination.
muscles, particularly in the intestine, which propagates in a Pores Refers to small channels or tiny openings that may be
wave down the muscular tube. microscopic, as in plant leaves, skin and the cell membranes,
Peritoneal The abdominal cavity and folds whose linings are and walls of other organisms such as parasites and bacteria,
composed of serous membranes. through which fluids may be absorbed or eliminated.
Peritonitis Inflammation of the layer of a membrane called Pork tapeworm Taenia solium infects the intestine and is
peritoneum that lines the inside of the abdominal cavity. contracted through eating raw or poorly cooked and contami-
Permethrin A topical insecticide used to treat for body and nated pork, and less often from beef or freshwater fish.
head lice, their nits, scabies, and to protect against various spe- Portal of entry Break in the natural immunity such as the
cies of ticks in the outdoors. protective skin, giving organism an avenue into the tissues of
Petroleum jelly Commonly called by the brand name Vase- the body.
line, petroleum jelly is a colorless-to-amber semisolid mixture Precystic form A trophozoite (motile form) stage often found
of hydrocarbons obtained from petroleum and is used as a lu- just before complete encystations.
bricant and in medicinal ointments. Prions A microscopic protein particle that is subviral (less
Phagocytosis Literally means “eating by cells” such as white than a virus) and lacking nucleic acid from which DNA is built,
blood cells that engulf pathogens as an immune function. is thought to be an infectious agent for mad-cow disease as well
Phylogenetic A map of the development or evolution of a as perhaps for certain other diseases.
organisms belonging to a particular group; studies similarities Procercoid Refers to the first stage in the aquatic life cycle
and possible common origins. of certain tapeworms where the elongate larval stage of some
Pica Abnormal craving for unnatural materials as part of the tapeworms develop in the body of a freshwater crustacean
diet, such as white dirt or clay. called the copepod.
Pinocytosis Refers to the ingestion of dissolved materials by Proglottids Segments of the cestode (tapeworm) that are
taking in liquids through the cell membrane; also called endo- capable of forming eggs and breaking off to infect other areas.
cytosis. The cytoplasmic membrane invaginates and pinches Progressive pernicious anemia Seriously grave blood
off small droplets of fluid that are retained in vesicles formed disease resulting in a continuing, devastating decrease in the
by this process. number of erythrocytes and accompanying fatty degeneration
Pinworms Threadworms that infect mostly children; scien- of the various tissues; commonly the victim exhibits a lemon-
tific name for this organism is Enterobius vermicularis. yellowish discoloration of the skin.
Plasmodium Genus of organism causing malaria in humans, Promastigotes Amistigotes undergo changes to become flag-
birds, and animals. ellated forms called promastigotes, an infective stage.
Platyhelminths Flatworms. Prophylactic Preventive measure to avoid infection
Plerocercoid Worm-like larval forms of certain tapeworm primarily.
that develop in secondary hosts. Prostatic secretions Prostatic secretions are expressed from
Pneumocystosis Infection with the Pneumocystis carinii the glands of males and the secretions are tested for evidence
(P. jirovecii) organism. of inflammation or infection by various microorganisms.
Pneumocystis carinii Opportunistic organism that Protein deficiency Often related to hookworm infections,
frequently infect those who are immunocompromised, where poor nutrition as well as loss of nutrition to the parasites
leading to pneumonia; often a condition found in AIDS lead to anemia and protein deficiency states, which results in
victims. emaciation and wasting.
Pneumonia An inflammation of the lungs, most often caused Protista This is a division under Kingdom Protoctista and
by infection. Bacteria, viruses, fungi, parasites, and even some Protoctista; eukaryotic one-celled living organisms as differen-
chemicals can cause pneumonia. tiated from multicellular plants and animals that includes many
Pneumonic form The pneumonic form of both the plague, of the parasitic protozoa.
caused by Yersinia pestis, and that of anthrax, caused by Bacil- Protoscolices One large cyst resulting from E. granulosus in-
lus anthracis, have pneumonic forms of the infections, and are fection may contain tens of thousands of protoscolices which,
gravely serious conditions. after ingestion, the protoscolices attach to the intestinal mu-
Polymerase chain reaction Technique to amplify or cosa where they develop into adult stages.
increase the numbers of a single or few copies of a strand Protozoa Member of Kingdom Protoctista and Protoc-
of DNA greatly, generating thousands of copies that can be tista, Division of Protista; includes unicellular animal-like
used for testing and for incorporating into other organisms. organisms.
Polymorphic nucleus Indicates a nucleus that may appear Pruritis Itching, burning, and sometimes tingling of the skin.
as segments such as in the polymorphonuclear leukocyte or Pseudomembranous colitis Term used for diarrheal
the segmented neutrophil. disease that often occurs in hospitalized patients with exten-
Polyvinyl alcohol (PVA) Used in a number of applications sive antibiotic therapy has enabled overgrowth of the bacte-
including a broad-use adhesive and as a water-absorbent sub- rium Clostridium difficile, which is identified by a toxin it
strate which when incorporated with mercuric chloride is used produces.