Source, Etc

The official thyroid gland is obtained from the sheep, Ovis aries, Linne (N.O. Ungulata).

Description

The thyroid gland is a highly vascular organ consisting of two almond-shaped lobes generally united towards their lower ends by a narrow bridge of tissue called the isthmus and forming a rounded projection on the trachea. It is distinguished from the surrounding tissue by its dark red colour and firm, coarsely granulated texture. Embedded in its substance are multitudes of closed vesicles containing a yellow glairy fluid termed colloid. This secretion contains the active constituent of the gland which probably passes into the system through the lymphatics. Each lobe of the fresh sheep's thyroid weighs about 2 grammes.

The lobes are usually removed separately, freed from surrounding fat and connective tissue, sliced or minced, and rapidly dried in a current of warm air at 30° to 40°. When sufficiently dry they are reduced to a coarse powder and the remaining fat removed by petroleum spirit. They are finally completely dried in a desiccator. Glands that are abnormal in size, or that exhibit cysts containing fatty matter when cut, should be rejected. The dry thyroid thus produced is a dull brown hygroscopic powder with a slight odour free from putresence.

Constituents

The active constituent appears to be a proteid body, thyreoglobulin, which can be dissolved out by a weak solution of sodium chloride and precipitated by the addition of ammonium sulphate. This substance contains uniformly 1.6 per cent. of iodine but no phosphorus. Boiled with dilute sulphuric acid it yields iodothyrin (thyroiodin) which contains from 9 to 14 per cent. of iodine, the constituent containing the iodine being apparently resistant to heat. Iodothyrin has also been supposed to be the active constituent. Fresh thyroids yield about 30 per cent. of dry, containing an average of 0.34 per cent. of iodine.

Uses

Thyroid gland is used in myxoedoema, goitre, obesity, and other cases in which a deficient production of the secretion is indicated.

Note

Parathyroid glands are small, four in number and lie close to or embedded in the thyroid. Their removal induces tetany, and certain forms of tetany are benefited by the use of preparations of the parathyroids.

The pituitary body, a gland situated at the base of the brain, forms one or more secretions of great physiological importance. It consists of a posterior, an intermediate and an anterior portion. Preparations of the posterior and intermediate portions, of the anterior portion and of the whole gland are employed medicinally. Extracts of the posterior and intermediate portions injected hypodermically raise the blood pressure and promote contraction of the uterus; the anterior lobe, dried and powdered, influences growth and development. From neither portion has an active constituent been isolated.

The spleen is a solid organ enclosed in a capsule. Its functions are not fully known, but it appears to be concerned with the protection of the body against disease by removing micro-organisms from the blood.

The thymus, or throat-bread, is composed of lobules united by connective tissues. Its secretion has a marked influence on sexual development.