INANITION OF THYKOID IN RATS 343 



3 to 10 weeks, the epithelial cells show a variety of changes in 

 structure, but it is doubtful whether there is in most cases any 

 marked decrease in the average volume of the cells. 



The cytoplasm, however, has undergone structural changes 

 similar to those described for the thyroid cells (though somewhat 

 less marked), its finely granular structure usually showing more 

 or less marked vacuoUzation or 'hydropic degejieration' (figs. 12, 

 13, 14). In some cases, however, especially with advanced karyo- 

 P3^cnosis, the cytoplasm may appear somewhat diminished in 

 amount, and with deeply-staining (eosinophile), coarsely granu- 

 lar structure. The cell-boundaries sometimes remain distinct 

 (fig. 12), but are frequently indistinct (figs. 13 and 14). 



Two distinct types of nuclear change occur (similar to those 

 found in the thyroid) . In the first or hypochromatic type (fig. 

 12) the nuc'ei appear vesicular, swollen and very lightly stained. 

 This type is relatively less frequent (as in the thyroid) and may 

 appear in all the cells over considerable areas (as in fig. 12), or 

 in scattered cells or small groups (as in fig. 14). This type of 

 nucleus probably represents an early stage of karyolysis, though 

 it is doubtful whether any nuclei actually reach dissolution in 

 the specimens studied. 



As in the thyroid, the more frequent type of nuclear change 

 in the parathyroid in young rats held at maintenance is in the 

 direction of hyperchromatosis, representing various stages of 

 karyopycnosis (figs. 13 and 14). For the most part, however, 

 the parathyroid nuclei do not go beyond the earlier stages, 

 merely showing a homogeneous background more deeply col- 

 ored so as to obscure the internal nuclear structure. In these 

 nuclei, there is little if any decrease in size, and this type fre- 

 quently occurs throughout practically the entire gland. Less 

 frequently more advanced stages of pycnosis are found, in which 

 the nuclei are diminished in size, with homogeneous deep stain 

 (fig. 13). The hyperchromatic and hypochromatic types of cell- 

 degeneration may sometimes occur intermingled, as in figure 14. 



No advanced stages involving karyorrhexis were found. 

 Neither mitosis nor amitosis was observed in any case. 



