THE THYROID AND PARATHYROIDS 271 



only to be observed in young individuals. Zimmerman 

 describes a double centrosome close to the free surface of the 

 cell. 



Occasionally one finds solitary cells in the interior of a vesicle. 

 These are normal epithelium cells, which have become separated 

 from the lining layer of the vesicle. Sometimes they are in a 

 good state of preservation ; mostly, however, they appear to 

 be in some stage of resorption. The nucleus stains faintly. 

 According to v. Ebner, leucocytes do not occur either in the 

 epithelium or in the cavity of the normal vesicle. 



As regards the contents of the vesicles, they are filled with 

 the yellowish sticky fluid which is observed to flow from the 

 surface when the gland is cut. The abundant presence of cells 

 and their debris in the interior of the vesicle may be due to post- 

 mortem changes. Verson states that the free surface of the cell 

 wall may be seen to project irregularly, and spheroidal, tena- 

 cious, and hyaline drops, which after some time coalesce in the 

 centre of the vesicle, gradually develop from the bodies of the 

 cells. 



Peremeschko found that the contents of the vesicles change 

 with the age of the animal. In young embryos there is a finely 

 granular mass, enclosing cells and nuclei. In larger embryos 

 one finds occasionally vesicles filled with transparent masses of 

 colloid ; in young animals this is the case with the larger 

 number of the vesicles, and in adults one rarely finds vesicles 

 without colloid. In adult animals the colloid substance 

 completely fills the cavity of the vesicles. 



Zeiss looks upon the colloid as nothing more than a concen- 

 trated form of the fluid originally appearing in the vesicles. In 

 this fluid he often finds a lump of colloidal material, around the 

 periphery of which new layers of colloid are being continually 

 laid down, until the entire cavity is filled with a compact mass 

 of colloid. The drops of secretion described by Peremeschko, 

 Zeiss considers to be simply appearances due to shrinkage. He 

 was never able to isolate the clear, transparent, unstainable 

 drops. 



Baber finds in the vesicles, in addition to a small quantity of 

 a clear substance, a solid mass which has retracted from the 

 wall of the vesicle. By staining with picrocarmine it shows a 

 finely granular structure, and is strongly differentiated by its 

 yellow colour from the red-stained epithelial wall. Hsematpxy- 



