Teratology

TERATOLOGY (from the Greek teras - wonder), the science that studies embryonic developmental abnormalities or malformations, concerning violations in the structure of the entire organism as a whole or its individual parts. The assumption of a completely special nature of the origin of such abnormalities, which does not occur in the normal development of the organism, led to Haller's formulation 'Monstra per fabricam alienam', which has survived to our time. - Subject of teratology. T. fundamentally encompasses all those prolonged - both structural and functional - changes in the organism that arose in the process of disrupted embryonic development and can undergo further development in the post-embryonic period. From this point of view, the subject of T. is any developmental abnormalities of the organism as a whole, its individual organs, tissues, and even cells, that arose as a result of disrupted mechanics of embryogenesis as a product of endogenously determined factors of embryonic development, or reactive processes of the embryo to external irritations (inflammatory, regenerative and other processes leading to malformation of individual parts of the organism). Some authors (W. Fischer) limit the subject of T. only to the first group of malformations. From a principled standpoint, any anomalies of constitution and congenital metabolic anomalies should also be subject to T. as functional developmental abnormalities that may not have a reflection in the structure of the organism or its individual parts. Practically, however, the subject of T. is limited only to structural malformations arising in embryogenesis and contrasted with normal proportions of parts in the organism. The methods of T. aim to clarify the formal and causal genesis, as well as to establish the time of origin ('teratogenetic terminal point' according to E. Schwalbe) of the developmental abnormality and its clinical significance. These methods require studying the totality of all conditions in which a particular malformation developed. The main importance is held by anatomical, embryological, comparative-anatomical and comparative-embryological methods. The basic prerequisite for these methods is knowledge of embryogenesis, organogenesis and histogenesis and the corresponding research techniques. Comparative anatomy often reveals the mechanism of origin of malformations by analyzing them from the point of view of Haeckel's biogenetic law ('atavism', 'Progonie' of Mathias). Comparative teratology (i.e., comparison of malformations in humans and animals) also contributed to clarifying the mechanism of many malformations. The study of conditions of pregnancy, prolonged or short-term violations of its physiological course [trauma to mother and fetus, pressure from a narrow uterus, abnormalities of the amnion (hydramnios, adhesions of the amnion), circulatory disorders of the fetus, etc.] is an essential part of the teratological method. Genetic analysis of malformations is necessary in each individual case, revealing the genotypic character of many of them that arose as a result of mutation (chondrodystrophy, polydactyly, syndactyly, prognathism, etc.). Methods of experimental zoology, methods of studying the mechanics of development, have contributed much valuable material to T. These methods revealed the mechanism of formation of certain malformations that arose in the order of correlational or relational connections between disorders in distant organs or systems. Thus, for example, experimental removal of rudiments of hind limbs in a tadpole, accompanied by subsequent disruption of the development of the central nervous system, reveals the possible connection with similar spontaneous malformations in humans (Darken). By the method of transplantation of individual organs or parts of an embryo to another embryo (Schaxel, Spemann, Born, Harrison, Mangold, Braus, etc.), it was possible to obtain the development of true or parasitic twins', formations similar to human teratomas and teratoid tumors (see Malformations). Lit.- see lit. to art. Malformations.