Neoplasia and its possible relationship to induction
Sherman, Joseph Donald
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The inductor is a substance that is found in the embryo. It functions to evoke cellular proliferation and cellular differentiation. The inductor is more active in some areas of the embryo than in other areas. These active induction areas may be called induction fields. The inductor was discovered in the embryo. Spemann, Vogt, and Mangold made significant contributions to the field of experimental embryology. The techniques developed by Vogt were supplemented by those developed by Spemann, and an inductoral process was demonstrated by Spemann. Three theories have been proposed to explain the nature of inductoral action. The Axial Gradient Theory was put forth by some investigators to explain the inductoral process. Other investigators maintained that the inductoral process depended upon an electrical potential. These investigators supported the Potential Difference Theory of induction. These two theories lack the support of most experimenters. Many phenomena cannot be explained by either the Axial Gradient Theory or by the Potential Difference Theory. A Chemical Theory of inductoral action was proposed. Most experimental evidence supports the theory that the inductoral process depends upon a chemical action. There is strong presumptive evidence that the inductor is not destroyed when the embryonic processes cease. The inductor may be present in every cell of the adult. The evidence from normal cell replacement and from wound healing supports the theory that the inductor is present in the adult. The experimental results from regeneration experiments, as well as the experimental results with adult tissue extracts, likewise support the theory that the inductor is present in the adult. There is also strong presumptive evidence that the inductor is present in the adult from the results obtained by experiments involving cancer of the gonads. The exact nature of the inductor is not known. The inductor may be either a sterol-like, carbohydrate-like, or a protein-like substance. There is good experimental evidence to support each of these three theories. The inductor may be liberated in many ways. It is thought to be released by viruses, carcinogens, cytolysis, and injury. It may also be liberated by metabolic processes. Many inductoral effects can be produced by synthetic inductors. The synthetic substances used to evoke an induction may either act as the natural inductor or cause the liberation of the natural inductor by injury or cytolysis. A neoplastic growth is one that exhibits proliferation , but it does not differentiate. Neoplastic growths may be produced by a cellular escape from the control of an induction field. When an induction field fails to control cellular proliferation and differentiation, but controls either one of these processes, there is a separation of the developmental processes. A separation of the developmental processes may result in a tumor or a cancer. Tumors are produced experimentally in embryos by processes that disrupt the normal action of the inductor. X-radiation, high and low temperatures, and delayed fertilization are a few of the processes that are used to separate the developmental processes and produce neoplasms. Teratoma of the adult and of the embryo can be explained by the separation of developmental processes within the adult and the embryo. The inductor may have been unable to exert its regulating and coordinating action. There are many similarities between neoplastic tissue and embryonic tissue. Many substances can induce neoplastic growth. Many substances can induce normal embryonic growth. Some substances possess the unique capacity of inducing embryonic growth as well as neoplastic growth. Estrogens and certain carcinogens can act as estrogens or carcinogens, but they may also act as inductors. Some carcinogens can evoke estrogenic effects. Estrogens can act as carcinogens. The effects, which these substances produce, depend upon the dosages of these substances used. It is also possible to change certain estrogens into carcinogens. Neoplastic growths may be produced by estrogens that have been altered chemically, and these altered estrogens may induce abnormal growths. It is important to consider the target area that is stimulated by the inductor. Normal inductor may act upon a disrupted target area and evoke an abnormal response. The nature of the inductor, as well as the nature of the target area, must be considered when the action of a carcinogen upon a tissue is studied. Regenerating tissue is similar to embryonic tissue. The regenerated tissue is stimlated by the inductor that is probably present in the adult. The inductor in an adult regenerate can alter tissue that has escaped from the control of the induction field. Such tissue can be induced to form normal tissue by the inductor present in the regenerate. Neoplasms be produced by an escape of one or more cells from the control of the residual embryonic inductor present in the adult. Such escaped cells proliferate wildly, but they do not differentiate and neoplasm results. There is also the possibility that neoplasms may be produced when the inductor is disrupted so that it cannot regulate mitotic division and differentiation. There is the further possibility that the physiological state of certain cells may be altered. These altered. cells may not respond to the stimulation of the normal inductor in the usual manner, since they may proliferate and not differentiate. A neoplastic growth could then result.
Thesis (M.A.)--Boston University