THE THYROID APPARATUS 31 



gland is not constant ; this is ascribed to the fact that thyroglobulin 

 is present in two forms, one of which contains iodine and one not. 

 The relative quantity of iodine to the whole amount of thyro- 

 globulin becomes smaller in proportion as the degenerative pro- 

 cess is more advanced. There is no iodine in the thyroglobulin of 

 goitres which are free from colloid substance. 



Oswald believes that thyroglobulin is formed in the interior 

 of the follicles, and that it is only after it emerges from them that 

 it becomes iodized ; or after iodization it may be excreted as a 

 colloid into the follicular space. He thinks that the production 

 of iodine-thyroglobulin is the physiological function of the thyroid 

 gland; that iodine thyroglobulin is the physiologically active 

 secretion ; and that the degree of activity depends upon the amount 

 of iodine present. Thyroglobulin obtained from goitres has a 

 physiological activity precisely similar to that obtained from 

 normal glands. Thyroglobulin which does not contain iodine does 

 not produce physiological results. 



It is Oswald's opinion that goitres, including the goitre of 

 Graves 's disease, are not to be regarded as a manifestation of 

 increased thyroid activity ; for, seeing how poor in iodine goitrous 

 glands are, the value of their function is diminished rather than 

 increased. They either do not form any secretion at all, or that 

 which they do form has a smaller physiological activity than that 

 of normal thyroid glands. F. Kraus, on the other hand, explains 

 the lack of iodine in the goitre of Graves's disease by a decrease 

 in the storage power of the gland, which thus parts with its 

 secretion too readily. Oswald is unable to deny that goitrous 

 glands are hyperactive, but he maintains that, though there is 

 increased secretory activity, the substance secreted has less 

 physiological value. 



ANATOMY OF THE PARATHYROID GLANDS. 



In development and function the parathyroid glands are 

 entirely independent of the thyroid, but anatomically they are 

 closely related to it. In man they are kidney-shaped bodies, 

 3-15 mm. long and 2-4 mm. broad and thick, and yellowish brown 

 to a brown-red in colour. As a general rule, they are four in 

 number and are situated in such a manner with regard to the 

 lobes of the thyroid, that it is customary to distinguish between a 

 posterior superior, and an inferior anterior parathyroid gland. 

 The upper body usually lies upon the dorsal surface, and at the 

 upper edge, of a nodulated process of the thyroid gland, known 

 as the pyramidal process, and it is found by following up the 

 inferior thyroid artery. The lower body is less constant in its 

 localization ; it may be situated at the lower edge of the pyramid, 

 or it may be found at the lower pole or on the medial surface of 

 the thyroid gland. Accessory parathyroids are sometimes present, 

 and these may extend downwards into the cavity of the thorax ; 



