. Comparative anatomy. Anatomy, Comparative. 456 COMPARATIVE ANATOMY for acid dyes such as eosin. The colloid is evidently a secretion of the cuboidal epithelium and is generally assumed to be a store of the hormone. Physiology. The most important, if not the exclusive, endocrinal secretion of the thyroid gland is an iodine compound thyroxine, the empirical chemical formula for which is C15H11O4NI4. A substance with identical properties has been made synthetically, and it is generally the synthetic drug which is used in medical practice. One function of thyroxine is to control metabolism, espe
. Comparative anatomy. Anatomy, Comparative. 456 COMPARATIVE ANATOMY for acid dyes such as eosin. The colloid is evidently a secretion of the cuboidal epithelium and is generally assumed to be a store of the hormone. Physiology. The most important, if not the exclusive, endocrinal secretion of the thyroid gland is an iodine compound thyroxine, the empirical chemical formula for which is C15H11O4NI4. A substance with identical properties has been made synthetically, and it is generally the synthetic drug which is used in medical practice. One function of thyroxine is to control metabolism, especially of the carbohydrates, a thirtieth of a grain increasing oxidation by one percent. Many commercial flesh-reducing preparations, therefore, contain thyrox- ine, often in dangerous quantity. It regulates also growth before birth,. iLOOD VESSEL Fig. 379.—A portion of a section of the thyroid gland enlarged, showing the secretory- epithelium and the colloid-filled follicles. through infancy, and at puberty, so that, in no small measure, we are what we are in virtue of our thyroid glands. Tadpoles fed with thyroid may become frogs no larger than flies. Excessive activity of the gland is a common malady, manifested by extreme nervousness, rapid pulse, insomnia, and basic metabolism above normal, so that the patient loses weight. In man, exophthalmic goitre is one of the common manifestations. As too much thyroxine speeds up the life processes, too little slows them down. Basal metabolism is low, so that the tendency is to put on fat. In the young, both growth and development are retarded; and if the deficiency is very great, a child, unless given thyroid artificially, may become an idiotic dwarf not unlike a cretin. Iodine is needed for the production of thyroxine, and in regions where iodine is lacking in the food, as in the central states of America and in the Alps, the glands may attempt to make up the deficiency by enlargement and increased secretion. This results in the
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