NORMAL MODE OF SECRETION IN THYROID GLAND 39 



multiplication of the epithelial cells, partly by increase of the col- 

 loid; after filling itself the vesicle discharges into the nearest 

 lymphatic vessel; finally the collapsed vesicle disposes itself in the 

 form of a number of little acini which repeat the process. 



Langendorff ('89) using the method of comparative study for 

 the elucidation of the secretory process in the cells of the thy- 

 roid gland, reached conclusions which, in some respects, confirm 

 and extend those of Biondi. He described two sorts of cells in 

 the gland which he designated, respectively, principal cells, and 

 colloid cells. The principal cells constituted the main mass of 

 the epithelium. They were cylindrical or columnar cells, of 

 variable height in different species and in different ages of the 

 same animal species. They possessed a reticular protoplasm, 

 with granules at the nodal points, and an oval or round nucleus 

 situated at the basal end of the cell. Like Biondi he saw occa- 

 sionally in these cells small hyaline spherules, but considered 

 them to occur very rarely. The colloid cells differed from the 

 principal cells by the hyahne, transparent appearance of their 

 cytoplasm. This cytoplasm browned with osmic acid, and, in 

 dyes, stained the same as the colloid content of the follicles. 

 He found all grades of transition between the colloid cells and the 

 principal cells. He regarded the colloid cells as elements en- 

 gaged in the secretion of colloid but did not commit himself 

 definitely to the opinion that, after a period of secretion, they 

 might return to the state of the principal cells. He was like- 

 wise in doubt whether they degenerated or not after secretion. 



V. Wyss (/89) studied the effects on the thyroid gland pro- 

 duced by poisoning with pilocarpine. He found in cats and dogs 

 that the gland after pilocarpine was large, turgid, and filled 

 with blood, and that the cells were larger, the nuclei less appar- 

 ent. The free ends of the cells were prolonged into processes 

 which were continuous with the colloid mass, and between these 

 processes were brilliant spherules of apparently fluid nature. 



Anderson ('94) confirmed V. Wyss' conclusions relative to the 

 effect of pilocarpine on the gland, and studied the structure of 

 the epithelial cells in young cats and rabbits at different periods 

 of time after injections of pilocarpine. He described, in the 



