The Effect of Thyroxin Upon the General Metabolism of the Intact Chick Embryo

MURRAY (1927) demonstrated a decrease in metabolic rate per gram of body weight with age in the normal chick embryo. The only attempt to alter the metabolic rate by the administration of thyroxin and to measure it manometrically is that of Hanan (1928). Using doses ranging from 0.033 to 0.025 microgram, Hanan detected a rise in the carbon dioxide production beginning at the seventh day. The weight accretion curve was not altered. This paper will report the effect of thyroxin injected prior to incubation on growth, differentiation and metabolic rate of the chick during the incubation period. The manometric respirometer used in this study was of the constant-pressure differential type employed by Romanoff (1941). In principle it is similar to that described by Dixon (1934) and originally suggested by Adam (1920). The eggs used in this work were of the Barred Columbian strain from the University of Connecticut poultry farm.