. Principles of modern biology. Biology. Ecology and Evolution - 579 RED BLOOD CORPUSCLES SPOROZOITE TROPHOZOITE SPOROZOITE SPOROZOITE-. GAMETOCYTES MICROGAMETE MACROGAMETE SPERM FERTILIZATION OF EGG STOMACH WALL PLASMODIUM ZYGOTE1 Fig. 30-7. Life cycle of one of the malaria parasites, a protozoan (Class, Sporozoa; Genus, Plasmodium). Note the three separate reproductive stages and the several adaptations to different conditions in two hosts. In man, the malarial fever flares up whenever swarms of the parasites emerge from one set of cor- puscles (which are destroyed) and pass, via the plasma,
. Principles of modern biology. Biology. Ecology and Evolution - 579 RED BLOOD CORPUSCLES SPOROZOITE TROPHOZOITE SPOROZOITE SPOROZOITE-. GAMETOCYTES MICROGAMETE MACROGAMETE SPERM FERTILIZATION OF EGG STOMACH WALL PLASMODIUM ZYGOTE1 Fig. 30-7. Life cycle of one of the malaria parasites, a protozoan (Class, Sporozoa; Genus, Plasmodium). Note the three separate reproductive stages and the several adaptations to different conditions in two hosts. In man, the malarial fever flares up whenever swarms of the parasites emerge from one set of cor- puscles (which are destroyed) and pass, via the plasma, into another set of corpuscles. (From Buchanan, Elements of Biology. Harper and Row.) skin, may be phagocytized by leucocytes, either locally at the site of the infection (p. 334), or in the lymph nodes, which filter the lymph as it drains from the infected area (p. 335). Or the parasite may be immobilized by encasement within a tough-walled cyst, which is constructed by the local connective tissues in response to the irritating presence of the foreign organism. But by far the most important defensive adaptation of organisms generally is a capacity to produce specific antibodies. Each antibody is a specific chem- ical compound that is formed by the tissues of the host and serves to limit the growth or to neutralize the toxins of some particular infective agent. Disease Resistance: Artificial Defenses. Vaccines and antisera are widely used in modern medicine to augment the natural antibody defenses of man and other animals. The vaccine with which an individual is inoculated (or vaccinated) always contains a specific antigen (p. 320) that stimulates the subject to produce the proper antibody. The vaccine may be an extract of an infectious organism; or the infectious organism itself may be used for the inoculation. But in the latter case, the infectious organism must first be killed or weakened (attenuated), or it must be selected from a nonvirulent strain. An antiserum, on the o
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