IXAXITIOX OF THYJ{()IL) IX HATS 339 



The cytoplasm is relatively small in amount, forming a nar- 

 row zone 1 to 2 micra in width around the nucleus. The cyto- 

 plasm is usually finely granular and pale reddish-violet in ap- 

 pearance (with Zenker fixation and haematoxylin-eosin stain). 

 Xo 'oxyphile' (eosinophile) cells are present. 



The nuclei of the parathyroid epithelium (fig. 11) vary con- 

 siderably. They usually appear elongated, the smaller rounded 

 forms perhaps representing cross-sections of ellipsoidal nuclei. 

 There is considerable ^'ariation in size (average about 4x6 micra) 

 and form. The nuclear outline frequently presents a notched or 

 lobulated appearance. 



In structure, the parathyroid nuclei are similar to those of the 

 thyroid, presenting a distinct, deeply-staining nuclear membrane, 

 and a faint nuclear network with usually one or two distinct 

 nucleoli (karyosomes), in a clear, light, homogeneous background 

 corresponding to the nuclear sap (karyolymph). Alitoses are 

 relati\'ely abundant at this stage, two or three being found in 

 each cross-section near the center of the gland. 



The parathyroid gland, like the thyroid, is in general fairly 

 uniform throughout in structure at this time, but certain irregu- 

 larities ma}^ appear, even at this age. In the most superficial 

 stratum of the gland, especially on the external free surface (not 

 in contact with thyroid) modified cells may appear. These 

 cells usually form small grouj^s of somewhat atrophic appear- 

 ance. The cytoplasm is more irregular, vacuolated or denser 

 and deeply-staining. The nuclei of these cells are generally 

 somewhat smaller than usual, often flattened, and with more or 

 less deeply-staining homogeneous appearance characteristic of 

 the earlier stages of pycnosis. Such atrophic cells rarely occur 

 except near the surface, and perhaps represent a mild form of 

 pressure-atrophy (as found also near the surface in the thyroid). 



The interstitial connective tissue forms a delicate, fibrous 

 stroma, like that of the thyroid, except that it is usualh' not so 

 highly vascular (fig. 11). In a few places, it is somewhat more 

 abundant, forming scattered, irregular, light streaks obser\'ed in 

 the interior of stained cross-sections. These streaks apparently 

 become more distinct in the older rats. 



