The Inhibitory Action of Insulin in the Early Chick Embryo

The list of effective teratogenic agents has become embarrassingly long: physical agents, metabolic inhibitors, vitamin deficiency, hypervitaminosis, and hormones, to mention only a few, are all known to produce congenital abnormalities. These substances have been administered at different times and in varying doses to nearly every group of animals, from amphibians to mammals, but there has been little effort to examine their mode of action. All too often, investigation ceases with the demonstration of a statistically significant number of abnormalities, enough to label the agent teratogenic. Sometimes a section of the work describes the histology of the lesions but does not indicate the primary action of the teratogen. Occasionally a drug has a well-recognized metabolic or chemical effect, e.g. cyanide on cytochrome oxidase, iodoacetate on triosephosphate dehydrogenase (Spratt, 1950), and we learn, by deduction, a little of the normal metabolism of development. Relatively few substances fall into this category, however.