342 Kojima 



on each side, embedded in the upper third of the thyroid substance near the 

 surface. It can be seen even by the naked eye as a more opaque point in 

 the substance of the thyroid. It would appear, however, that there are 

 occasionally aberrant parathyroids in these animals, and one is not perfectly 

 certain that all parathyroid tissue has been removed even if the two obvious 

 parathyroids are completely excised. 



Structure of the Normal Parathyroid of the Rat. — The para- 

 thyroid consists of a large number of small cells which are usually com- 



FlG. .3. — Section showing adjacent portions of thyroid and parathyroid of male rat 

 fed with an addition ot O'l grm. of sodium iodide per diem to its ordinary 

 food during five days. Microphotograph ; magnified 200 diameters. Htema- 

 toxylin-eosin preparation. 



The thyroid vesicles are distended with colloid. Their lining epithelium 

 cells are flattened, but rather less so than in the thyroid shown in the thyroid- 

 fed animal (fig. 2). The parathyroid is less com])act than normal (cf. fig. 1), 

 but more so than in the thyroid-fed animal. 



pactly arranged. Each cell has a clear protoplasm which is comparatively 

 small in amount. The cell-nuclei vary in shape, being round, oval, or oblong, 

 but their size is fairly constant (about 5/x). They stain distinctly by 

 hsematoxylin, and contain fine chromatin granules. The cytoplasm is 

 usually faintly stained by eosin. Occasionally there appears a vesicular- 

 like arrangement of the cells, but this is rare. The parathyroid tissue is 

 always quite sharply marked off from that of the thyroid, with connective 

 tissue between. 



Effect of Administration of Thyroid and Parathj^roid, 

 and of certain Sodium and Potassium Salts. 



Changes in Thyroid. — After thyroid feeding most of the vesicles 

 are large and distended with colloid. The epithelium cells lining them are 



