ABSTRACT
In the developing chick embryo, liver glycogen appears on the sixth day of incubation. The glycogen content increases from the sixth day, but decreases on the twelfth day before increasing again.
This decrease on day 12 might be related to the onset of thyroid activity, which would be responsible for an increased rate of utilization of the substrates.
An antithyroid drug, thiourea, has been injected on day 6·0. The liver glycogen concentration of the thiourea-treated chick embryos was determined from the tenth to the fifteenth days and compared with that of the control embryos.
On days 11 and 12 the liver glycogen concentration of the injected embryos is higher than that of the controls.
On day 13 the liver glycogen level of treated embryos decreases; this decrease might be correlated with possible functional activity of the thyroid glands if their biosynthesis is no longer inhibited by the thiourea injection or with thyroid hormones possibly coming from the yolk.
On days 14 and 15 no difference is observed between the liver glycogen content of the thiourea-treated embryos and that of the controls.
