teratology(redirected from Teratogenic effect)
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the science of monstrosities. The teratology of animals deals with deviations from normal body structure caused chiefly by disturbances in embryonic development. According to the type of manifestation, monstrosities are either insignificant deviations that exceed the variations observed within the norm, or severe deviations from normal body structure that often make the organism nonviable.
The scientific study of monstrosities in animals and man has been aided by the establishment in many countries of teratological collections, which have made it possible to compare and classify monstrosities. One of the first such collections was established in the late 17th century by the Dutch anatomist F. Ruysch. Peter I the Great became acquainted with this collection during his sojourn in Holland in 1697–98, and in 1717 he purchased it. In 1704 he issued a decree prohibiting the killing of monsters and ordering that they be reported to the Monastyrskii Prikaz. A decree of 1718 stipulated that all living and dead monsters, both human and animal, be brought to the St. Petersburg Kunstkamera. This led to a rapid enlargement of the Kunstkamera’s teratological collection, which was open to visitors.
Beginning in the late 1760’s, the Kunstkamera’s collection was studied by C. F. Wolff. The most important of Wolff s teratological studies was his description of a two-headed calf. The description was supplemented by a memoir, The Origin of Monsters (1773), which affirmed the natural origin of monsters and proved that such double monsters as xiphopaguses, pygopaguses, and thoracopaguses result not from the joining of two embryos but from the partial separation of a single embryo. Teratological collections were later studied by the academicians of the St. Petersburg Academy of Sciences P. A. Zagorskii and K. M. Ber. K. F. Rul’e also stressed the natural origin of monstrosities.
In the early 19th century, scientists attempted to produce monstrosities artificially in order to study their origin. The first attempt to apply the experimental method to teratology was made by E. Geoffroy Saint-Hilaire. Similar experiments were continued by the French scientists I. Geoffroy Saint-Hilaire and J. B. Dumas and by the Swiss physician J. L. Prévost. Systematic studies of monstrosities were later made in France by G. Dareste and in Russia by P. I. Mitrofanov.
Attempts to produce monstrosities artificially were particularly widespread during the first half of the 20th century, when experimental embryology underwent rapid development. Mechanical influences on the dividing egg cell of amphibians and fishes, and later of birds and mammals, resulted in the production of various monstrosities. W. Roux and H. Spemann produced twins joined at the head and tail extremities, and Spemann and D. P. Filatov produced cyclopia (the presence of only one eye), a deformity resulting from impaired brain structure. O. Hertwig produced monstrosities experimentally by subjecting the dividing egg cell to high or low temperatures. J. Loeb produced monstrosities by means of radiation and by changing the chemical composition of the environment. Other monstrosities were produced by interfering with the normal respiration of the embryo. During the first half of the 20th century, much was learned about the teratogenic influence of somnifacients, antibiotics, and insecticides.
Some monstrosities are hereditary. In man, dominant monstrosities include congenital dislocation of the hip, harelip, and cleft palate; recessive monstrosities include deaf-mutism, flat-footedness, and total albinism.
Modern teratology studies the causes and origins of hereditary and nonhereditary congenital pathological states and developmental defects. It seeks to prevent congenital developmental defects in animals and man. The detection of teratogens is of importance in the prevention of such defects. Consequently, all new medicines are tested on animal embryos for the possible presence of teratogens. Toxic chemicals used in agriculture are tested as well. Teratology is also of importance in the biology of development, since knowledge of the deviations caused by teratogens or mutant genes is a means of discovering the motivating forces and controlling mechanisms of normal embryonic development in animals and man.
The teratology of plants deals with nonhereditary and hereditary monstrosities, anomalies, and developmental defects, which result in changes in the number, size, arrangement, and external and internal structural of organs. The causes of plant malformations include infections with viruses, mycoplasmas, bacteria, or fungi as well as damage effected by nematodes, ticks, or insects. Other causes of plant malformations are hybridization, ionizing radiation, geophysical factors, chemical growth regulators, fertilizers, pesticides, industrial wastes, minerals, low and high temperatures, excessive or insufficient water and light, and mutation. Plant malformations include gigantism, dwarfism, double flowering, witches’-brooms, prolification of flowers and of inflorescences, fasciation, and impaired embryonic development. Many teratological changes are caused by smut and white rust of corn, dwarf smut of wheat, follicular disease of plum, and tomato big-bud virus.
Knowledge of plant malformations aids in the study of the morphological evolution of plants and in the establishment of laws of comparative plant pathology. Such knowledge is also useful in selective breeding and in determining means of increasing the biological productivity of plants and of protecting plants from pests and disease. Knowledge of plant malformations is of value in the development of efficient methods for utilizing chemical agents in agriculture and forestry; in seeking useful minerals; in biological studies of chemical compounds and physical influences; and in determining the detrimental effects of industrial contaminants.
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L. IA. BLIAKHER, A. P. DYBAN, and E. I. SLEPIAN