INANITION OF THYROID IN RATS 341 



In the parathyroid at 10 weeks, the structure is essentially 

 the same as at 3 weeks (fig. 11), no important change in the 

 appearance or average size of the cells being observed. Mitoses 

 appear somewhat less frequently, only 1 or 2 in a section. The 

 atrophic or degenerated types appear usually somewhat more 

 frequently and more pronounced in character, however. They 

 most commonly appear in the superficial stratum, especially at 

 the exposed surface (not in contact with thyroid); but occa- 

 sionally in the interior also, usually in scattered areas. The 

 nuclei of these cells are usually deeply-staining and pycnotic, 

 though vesicular karyolytic forms also occur. The cytoplasm 

 in these atrophic types is usually rarefied and vacuolated in ap- 

 pearance, but occasionally somewhat coarsely granular and 

 deeply-staining (eosinophile), suggesting in some respects the 

 'oxyphile' type described as normal by some authors for the 



Fig. 11 A small portion of the parathyroid gland .shown in figure 1 (rat 8 

 9.47, normal 3 weeks), magnified to represent the details of the normal histologi- 

 cal structure (which is essentially the same as at 10 weeks). Epithelial cells in 

 irregular masses; cytoplasm granular, scanty in amount; nuclei irregularly elon- 

 gated in appearance. Stroma scanty, vascular. (X 750.) 



Fig. 12 A small portion of the parathyroid gland shown in figure 4 (rat No. 

 S 11.63, held at maintenance from 21 to 72 days of age), magnified to show details 

 of histological structure. This area represents the hypochromatic (incipient 

 karyolytic) type, which is relatively infrequent. The nuclei appear light and 

 swollen. The cytoplasm here is apparently not reduced in amount, but shows 

 tendency to vacuolization and disappearance of the normal granulation. Stroma 

 normal. (X 750.) 



Fig. 13 A small port on of the parathyroid gland shown in figure 5 (rat No. 

 S 5.10, held at maintenance from 21 to 67 days of age), magnified to show the de- 

 tails of histological structure. This area represents the typical hyperchromatic 

 type (various stages of karyopycnosis) . Cytoplasm more or less reduced in 

 amount, with marked vacuolization ('hydropic degeneration'). Stroma nor- 

 mal. (X 750.) 



Fig. 14 A small portion of the parathyroid gland shown in figure 6 (rat No. 

 S 11.64, held at maintenance from 21 to 73 days of age), magnified to show the 

 details of histological structure. This area represents a somewhat advanced 

 stage of degeneration, which frequently involves small, scattered masses, but is 

 rarely extensive. The nuclei are partly of the hypochromatic (karyolytic), and 

 partly of the hyperchromatic (karyopycnotic) type. Around the former, the 

 cytoplasm is usuallj' vacuolated ('hydropic degeneration'); while arovuid the 

 latter type cytoplasm appears reduced in amount, deeply-staining (eosinophile) 

 and frequently coarsely granular in appearance. (X 7.50.) 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 19, NO. 2 



