Effect of Age and Season on the Thyroxine Secretion Rate of White Leghorn Hens

THE theory has been suggested that the inheritance for the several valuable characters of domestic animals such as rapid growth, high fertility, large milk secretion and large total egg production is realized in major part, or is brought to fulfillment in animals and birds by the ability of the various endocrine glands to secrete optimum amounts of their hormones which play roles in stimulating the development of the character under consideration. However, just as environment and physiological factors influence the demonstration of quantitative characters, so one would expect that these same factors would influence the hormone secretion rate of the endocrine glands which may be involved. In order to obtain verification of this working hypothesis, it is necessary to develop methods of measuring the hormone secretion rate of the various endocrine glands. When this is accomplished it will be possible to determine the relation between the hormone secretion rate and . . .