EFFECTS ON THE THYROID AND PARATHYROID GLANDS 439 



marked increase in the weight of the thyroid in adult fasting rats, in disagree- 

 ment with the results above mentioned. 



A special study of the histological effects of inanition upon the thyroid gland 

 of the albino rats was made by Jackson ('16), the results being summarized 

 as follows: 



"In young rats held at maintenance for several weeks (and hence in a 

 condition of chronic inanition), the histological changes in the thyroid are 

 varied. The follicular epithelium is atrophied, with reduction in height. 

 The nuclei are rarely hypochromatic (various stages of karyolysis), but hyper- 

 chromatosis is more typical, the nuclei usually presenting some stage of pycnosis. 

 In the earlier stages the nucleus may be nearly normal in size and structure, 

 excepting a pale, homogeneous coloration of the nuclear background. In 

 more advanced stages, the nucleus diminishes in size, with deepened coloration, 

 forming a dense, deeply-staining, homogeneous mass (typical pycnosis). In 

 extreme cases the nucleus becomes fragmented (karyorrhexis). Neither 

 mitosis nor amitosis is found. 



"The cytoplasm is usually reduced in amount considerably more than the 

 nucleus. The cytoplasm may show no marked change in structure (simple 

 atrophy), but usually becomes rarefied, with a marked vacuolization ('hydropic 

 degeneration') and loss of the normal granulation. This is especially marked 

 in the few cells where the cytoplasm has lost but little in volume. In some 

 cases the cytoplasm may become homogeneous ('colloid' type) and in advanced 

 stages may disintegrate, forming irregular, deeply-staining (eosinophile) 

 masses of varied appearance. 



"The intrafollicular colloid may show no abnormal changes. Advanced 

 stages of degeneration in the follicular epithelium, however, are accompanied 

 by dissolution and disintegration of the colloid. The colloid is often replaced 

 by desquamated epithelial cells in various stages of degeneration, and the entire 

 follicle may collapse into an irregular mass. 



"The interfollicular connective tissue (stroma) usually shows no very 

 marked change in structure, but is often increased in volume by an infiltration 

 of ground substance, giving a somewhat edemic appearance. On this account, 

 the whole thyroid gland may show but little loss in absolute weight, although 

 there has been a marked atrophy of the parenchyma. 



"In the adult rats subjected to acute and chronic inanition, the changes 

 in the structure of the thyroid gland are likewise varied, but in general similar 

 to those found in the younger rats. The interpretation of the changes in the 

 older rats is more difficult, on account of the frequent occurrence in the normal 

 (control) rats of degenerative changes somewhat similar to those found in 

 advanced stages of inanition. 



"These changes, involving desquamation and degeneration of the follicular 

 epithelium, have frequently been observed in the thyroids of rats both normal 

 and under various abnormal conditions. They also occur as pathological 

 changes in various other glands. It is suggested that the similarity of these 

 cell-changes may possibly be due to cell-inanition as a common underlying 

 factor." 



