340 DUCTLESS GLANDS. 



Chemical Composition. An analysis of an adult thyroid 

 gives a percentage of 82.24 of water, 17.66 of organic and 0.1 

 of inorganic constituents ; in that of an infant the figures were, 

 77.21, 22.35, and 0.44 respectively. Like the spleen, it is alkaline 

 during life and acid after death, the acidity being due to the same 

 cause the formation of sarcolactic acid. Fatty acids, xanthin, 

 hypoxanthin, and other extractives have also been obtained 

 from it. 



The constituents which possess the greatest importance are 

 those of a proteid nature, for upon them it is believed depend 

 some of the remarkable powers with which this gland is endowed. 

 Among these are thyreoproteid and thyreo-antitoxin (C 6 H U N 3 O 5 ). 

 A substance has also been found in the thyroid, principally com- 

 bined with a proteid, although also free, called thyro-iodin and 

 iodo-thyrin, containing 9.3 per cent, of iodin and 0.56 per cent, 

 of phosphorus. The amount of iodin in each gram of the human 

 adult thyroid varies from 0.3 to 0.9. 



Structure. The thyroid has a capsule of connective tissue 

 which sends off septa or trabeculce that enclose the thyroid vesicles 



--- Lumen of follicle. 

 Connective tissne. 



1 Epithelium of follicle. 



J 



FIG. 183. From section through thyroid gland of child (Bohm and Davidoff). 



(Fig. 183), each of which is lined by cubical epithelium and con- 

 tains viscid, colloid liquid, yellowish in color, which is coagulated 

 by alcohol and stained with hematoxylin, and is doubtless secreted 

 by these cells. Red blood-corpuscles in various stages of disinte- 

 gration and white corpuscles are also found in these vesicles. 

 The color of the colloid material is probably due to hemoglobin. 

 Around the vesicles is a plexus of capillary blood-vessels, 

 which is also found between the vesicular epithelium and the 

 endothelium of the lymph-spaces, which latter surround the vesi- 

 cles and communicate with lymphatic vessels. Colloid material, 



