. The endocrine organs; an introduction to the study of internal secretion . —Section of thyroid, human, injected. (Major.) Highly magnified. The closerelation of the capillaries to the vesicles is shown. colloid is insoluble in alcohol, water, or ether; when coagulated it isreadily stained by eosin, less easily by hasmatoxylin. In fixed sectionsit often appears shrunken away from the epithelium. It is believed tobe formed from granules which are produced within the cells, and whichbecome changed and dissolved on extrusion. Doubtless it contains theactive principles of the secretion, and proba
. The endocrine organs; an introduction to the study of internal secretion . —Section of thyroid, human, injected. (Major.) Highly magnified. The closerelation of the capillaries to the vesicles is shown. colloid is insoluble in alcohol, water, or ether; when coagulated it isreadily stained by eosin, less easily by hasmatoxylin. In fixed sectionsit often appears shrunken away from the epithelium. It is believed tobe formed from granules which are produced within the cells, and whichbecome changed and dissolved on extrusion. Doubtless it contains theactive principles of the secretion, and probably forms a storehouse whencethey can be extracted as required by the organism. A close relationship exists between the size and structure of the thyroidand the state of general nutrition of the animal. The effect of variationsof diet upon the thyroid has been studied in rats by Chalmers Watson (seefigs. GA and 6fi), who has shown that all transitions from an active or super-active organ with highly developed columnar epithelium and irregular Development of Thyroid 15. Magnified 250 FIG. 6A. — Section of thyroid of wild rat. diameters. The vesicles are seen to be distended withcolloid and the cells flattened. (Chalmers Watson.) large vesicles and without any great accumulation of colloid, to a gland with flattened epitheliumand vesicles greatly dis-tended by colloid are ex-hibited under the influenceof different nutritive sub-stances in the diet: theformer conditions being, in O the rat, typically seen whenthe animals have been fedupon a mixed food such asbread and milk; the latterwhen the diet has beencomposed of lean feeding of rats o O with lean meat led eventu-allv to a shrinking in size t> O of the vesicles and of thewhole organ, these changesbeing associated with dry-ness of skin, falling off ofhair, and other evidencesof ill-health; in carnivora results of this kind were not observed. Development.—The thy-roid is originally developedlike an ordina
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