342 C. M. JACKSON 



parathyroid of various animals (including man). Sometimes 

 spaces are seen between the larger bundles of connective tissue 

 and the adjacent parenchyma. These spaces somewhat re- 

 semble in appearance the paratrabecular and subcapsular lymph- 

 sinuses in lymph-nodes. 



In the older and adult animals, the parathyroid gland shows 

 essentially the same structure as described at 10 weeks. The 

 cells average perhaps shghtly larger, the nuclei being typically 

 elliptical and averaging between 4x6 and 5x7 micra. The 

 cytoplasm forms a hght granular zone 1 to 2 micra in width. 

 Mitoses are not found in the adult rats. The atrophic or de- 

 generative types of cells occur frequently, though usually in 

 limited, scattered areas, especially near the exposed surface of 

 the parathyroid. 



b. Structure of the parathyroid glands in young rats held at 



maintenance 



If in the rats held at maintenance (constant body-weight) 

 from the age of 3 to 10 weeks the dimensions of the parathyroid 

 glands be compared with those of the controls at 3 and 10 weeks 

 (table 1), it appears that the parathyroid has not shrunken in 

 size during the experiment. On the contrary it has even ap- 

 parently increased so that the dimensions are nearly as large as 

 those of the full-fed controls of the same age but several times 

 larger in body-weight. As shown in table 1, the average diame- 

 ter of the normal parathyroid at 3 weeks is about 0.40 mm., at 

 10 weeks, 0.54 mm.; in maintenance 3 to 10 weeks, 0.49 mm. 

 Thus the parathyroid in young rats held at maintenance be- 

 comes relatively very large in comparison with the thyroid (which 

 usually decreases somewhat), as is apparent upon comparison 

 of the parathyroids in figures 1 and 3 with those in figures 4, 5 

 and 6. 



The changes in the histological structure of the parathyroid 

 gland during inanition are on the whole less marked than in the 

 thyroid gland, although in most respects similar in character. 

 In the parathyroids of rats held at maintenance from the age of 



