310 CM. JACKSON 



The follicles at this time are chiefly oval or rounded in outline 

 and vary mostly from 20 to 70 micra in diameter. The larger 

 follicles are rather infrequent and somewhat uniformly scattered, 

 but are usually more frequent near the surface of the gland. 

 Those shown in figure 2 are of average size. 



The finer structure of the thyroid gland is shown in figure 2. 

 The cells of the follicular epithelium are approximately cuboidal 

 in form (in some cases low columnar; in others, especially in the 

 larger peripheral follicles, somewhat flattened). In height, they 

 range chiefly between 8 and 15 micra, the average being 10 to 

 12 micra. The inner and outer cell walls are sharply distinct ; 

 the intercellular boundaries are less distinct and sometimes 

 absent. 



The cytoplasm of the follicular cells (fig. 2) is filled with mod- 

 erately fine granules, reddish violet in color (with Zenker fixation 

 and haematoxylin-eosin stain). The granules are usually some- 

 what uniformly distributed. They are not densely packed, but 

 are sometimes arranged so as to give an indefinite reticular form, 

 apparently intermingled with small, clear vacuoles. Some of 

 these vacuoles (though not all) may correspond to the minute 

 fat droplets or granules described in the thyroid cells by Erd- 

 heim ('03) and Traina ('04). The cells present a fairly uniform 

 appearance, and there is nothing to indicate any di^''ision into 

 the 'chief and 'colloid' cell types of Langendorff. 



The nuclei of the follicular cells are spherical or slightly ovoidal 

 (ellipsoidal) in form, the diameters varying from 4 to 7 micra, 

 usually 5 or micra. The nuclear membrane is distinct and 

 stains deeply. There are usually one or two larger nucleoli 

 (karyosomes) and several smaller granules; and a fine, ]:)aler nu- 

 clear network, often indistinct, with a very pale bluish, homo- 

 geneous nuclear background, corresponding to the nuclear sap 

 (karyolymph). The nuclei shown in figure 2 are typical, though 

 in the larger peripheral follicles with slightly flattened cells the 

 nuclei may also be somewhat more flattened and slightly hyper- 

 chromatic. Cells in mitosis are relatively freciuent, 5 having 

 been noted in one entire cross-section of one lobe, and () or 8 in 

 another. 



