germ theory

(noun)

The germ theory of disease, also called the pathogenic theory of medicine, is a theory that proposes that microorganisms are the cause of many diseases. Although highly controversial when first proposed, germ theory was validated in the late 19th century and is now a fundamental part of modern medicine and clinical microbiology, leading to such important innovations as antibiotics and hygienic practices.

Related Terms

Examples of germ theory in the following topics:

  • Pasteur and Spontaneous Generation

    • This was one of the last and most important experiments disproving the theory of spontaneous generation.
    • Ultimately, the ideas of spontaneous generation were displaced by advances in germ theory and cell theory.

  • Antibiotic Discovery

    • Louis Pasteur was a French microbiologist and chemist best known for their experiments supporting the Germ theory of disease, and for his vaccinations, most notably the first vaccine against rabies.

  • History of Epidemiology

    • One of the earliest theories on the origin of disease was that it was primarily the fault of human luxury.
    • In the middle of the 16th century, a doctor from Verona named Girolamo Fracastoro was the first to propose a theory that these very small, unseeable, particles that cause disease were alive.
    • The development of a sufficiently powerful microscope by Anton van Leeuwenhoek in 1675 provided visual evidence of living particles consistent with a germ theory of disease.

  • Modern Microbiology

    • Pasteur is most famous for his series of experiments designed to disprove the then widely held theory of spontaneous generation, thereby solidifying microbiology's identity as a biological science.
    • Koch is best known for his contributions to the germ theory of disease, proving that specific diseases were caused by specific pathogenic microorganisms.

  • History of Microbiology: Hooke, van Leeuwenhoek, and Cohn

    • Thus, Pasteur dealt the death blow to the theory of spontaneous generation and supported germ theory instead.

  • Gastrulation

    • During gastrulation, the embryo develops three germ layers (endoderm, mesoderm, and ectoderm), which differentiate into distinct tissues.
    • These three germ layers are known as the ectoderm, mesoderm, and endoderm.
    • It is followed by organogenesis, when individual organs develop within the newly-formed germ layers.
    • In amniotes such as humans, gastrulation occurs in the following sequence: (1) the embryo becomes asymmetric, (2) the primitive streak forms, and (3) cells from the epiblast at the primitive streak undergo an epithelial to mesenchymal transition and ingress at the primitive streak to form the germ layers.The ectoderm gives rise to epidermis, and also to the neural crest and other tissues that will later form the nervous system.
    • Formation of the three primary germ layers occurs during the first 2 weeks of development.

  • Tissue Development

    • The endoderm is one of the germ layers formed during animal embryogenesis.
    • The mesoderm germ layer forms in the embryos of triploblastic animals.
    • It emerges first and forms from the outermost of the germ layers.
    • Image illustrates the types of cells produced by the mesoderm (middle germ layer) of the developing embryo.
    • Image illustrates the types of cells produced by the endoderm (inner germ layer) of the developing embryo.

  • Animal Characterization Based on Features of Embryological Development

    • Most animal species undergo a separation of tissues into germ layers during embryonic development.
    • These germ layers are formed during gastrulation, developing into the animal's specialized tissues and organs.
    • Animals develop either two or three embryonic germs layers .
    • Each of the three germ layers in a blastula, or developing ball of cells, becomes particular body tissues and organs.
    • During embryogenesis, diploblasts develop two embryonic germ layers: an ectoderm and an endoderm.

  • Cytotoxic Autoimmune Reactions

    • The X-inactivation skew theory, suggesting the female-high tendency, and proposed by Princeton University's Jeff Stewart, has recently been confirmed experimentally in scleroderma and autoimmune thyroiditis.
    • Autoimmunity is often caused by a lack of germ development of a target body and, as such, the immune response acts against its own cells and tissues.
    • Another theory suggests the female-high tendency to get autoimmunity is due to an imbalanced X chromosome inactivation.
    • The X-inactivation skew theory, proposed by Princeton University's Jeff Stewart, has recently been confirmed experimentally in scleroderma and autoimmune thyroiditis.

  • Testicular Cancer

    • Although testicular cancer can be derived from any cell type found in the testicles, more than 95% of testicular cancers are germ cell tumors .
    • Most testicular germ cell tumors have too many chromosomes, and most often they are triploid to tetraploid.
    • About half of germ cell tumors of the testis are seminomas.