Biochemical studies on the skeleton of insulin-induced micromelia in chickens.

Various statistical reports attest to the high incidence of congenital malformations. Investigations by Hertig & Rock [5] indicate that a comparatively large number of early human embryos display malformations of such a character that normal development could hardly be expected. Among 26 human foetuses less than 16 days old, obtained during surgery on the uterus, no less than 12 or 47% displayed severe abnormalities. MacGregor [9] reviewed 1053 stillbirths and neonatal deaths and found that 20 % of stillbirths and 10% of neonatal deaths were directly attributable to gross congenital malformations. The frequency of congenital malformations is also relatively high among the survivors (Table 1). The cause or causes of congenital malformations are more or less unknown. They are, however, attributed to genetic factors as well as to factors influencing the environment of the embryo. During the last few decades experimental teratogenesis has considerably increased our knowledge of the relation of congenital malformations to factors influencing the en-