ABSTRACT
An attempt was made to determine in the developing fowl embryo whether injections of thyroxin into the incubating egg would lead to a modification of the processes of sexual differentiation.
The injections into the air space were made during the 3rd day of incubation, that is, at a time before the differentiation of the gonads in the two sexes can be demonstrated.
Of the 190 eggs injected with thyroxin, 39 embryos survived of which 12 were markedly affected, reduced size of embryos being regarded as an indication of a marked hyperthyroidism which has resulted in an increase in the metabolic rate.
No effect on the processes of sexual differentiation in either sex was found.
The effect of the injections was not apparent before the 1 ith day. It will be attempted in a further series of experiments to determine whether this is a specific reaction of the thyroxin or whether it is due to mechanical hindrances to the absorption of the thyroxin into the foetal circulation until a considerable time after the injection.
These experiments can not at present lead to any definite conclusion as to the relation between increased metabolism and the processes of sexual differentiation.
