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This book consists of several sections. The introduction is an important part of this text because it gives Dr. Shepard's balanced and conservative approach to the use of information in the literature, and the many difficulties that a scientist encounters in trying to interpret the teratologic literature and apply it to the human species. Dr. Shepard defines a congenital defect as having "its genesis during embryonic or fetal development and consists of a major or minor deviation from normal morphology or function." The only argument that some teratologists have with this definition is that the deviation from normal morphology or function should be irreparable. Some drugs and chemicals can produce functional or even morphological deviations in the embryo that can be totally corrected during the growth and development of the organism, either in utero or during the postpartum or adolescent period.
There is a carefully prepared table comparing the embryonic
BRENT RL. The Catalog of Teratogenic Agents.. Am J Dis Child. 1974;128(1):121. doi:10.1001/archpedi.1974.02110260123038