270 THE DUCTLESS GLANDS 



vesicles are of roundish, long, oval, or polyhedral form, but 

 occasionally one meets with forms somewhat resembling the 

 tubules of alveolar glands, only that they are closed at both 

 ends ; these have sometimes side branches, or two or three 

 large vesicles may freely communicate with each other. In 

 many lobules one finds in addition to the vesicles solid cords 

 and nests of epithelium cells. These are more numerous in the 

 young and developing thyroid. 



The ensheathing capsule of the organ and the interlobular 

 connective tissue consist of bundles of white fibres with 

 numerous elastic fibres. This connective tissue carries numerous 

 bloodvessels and lymph vessels into the interior of the lobules, 

 and finally surrounds the vesicles of the gland substance. 'The 

 vascular connective tissue comes into immediate contact with 

 the epithelial lining of the vesicles. It is said that there is no 

 membrana propria ; the vesicle is enclosed by very fine bundles 

 of connective-tissue fibres, outside of which is the endothelium 

 of the lymph spaces. 



The epithelium cells lining the vesicles are of a fairly uniform, 

 cubical, or columnar form, 9 ^ to 13 ju, in height. They tend to 

 become flatter in old age, but cylindrical cells are not un- 

 commonly found, even in the adult. When examined in 0-75 

 per cent, normal saline, the epithelial cells of the human thyroid 

 show, in most instances, a number of granules of varying size. 

 These are chiefly aggregated in the part of the cell next to the 

 cavity of the vesicle ; they are highly refractive, and show a 

 characteristic greenish tinge. These are apparently of a fatty 

 nature ; but, in addition to these, there are found in the cells 

 smaller granules of a different character. The larger granules 

 appear to be characteristic of human thyroid. 



According to Langendorff, the epithelium cells are of two 

 kinds " Hauptzellen " and " Colloidzellen." In osmic-acid 

 preparations stained with the Ehrlich-Biondi mixture, the 

 former are unstained, while the latter appear red with green 

 nuclei. According to v. Ebner, these do not represent two 

 distinct varieties of element, and there is nothing in the vesicular 

 epithelium corresponding to the two kinds of cell in the glands 

 of the stomach. The cell protoplasm shows a retiform struc- 

 ture, with frequent longitudinal striation. The nuclei are 

 spherical, have a homogeneous appearance, or show a very fine 

 chromatin network. As in other gland epithelia, mitosis is 



