322 C. M. JACKSON 



In no case was cell-division, either mitotic or amitotic, ob- 

 served in the thyroid gland of the young rats held at mainten- 

 ance for several weeks. 



The colloitl in the thyroid of the maintenance rats is usually 

 nearly normal in appearance (figs. 7, 8), excepting those follicles 

 with advanced degeneration of the epithelium. In these (fig. 9), 

 especially where the epithelial cells are desquamated, the colloid 

 becomes more or less granular and fragmented, finally appear- 

 ing as irregular masses among the cellular debris or disappearing 

 altogether. The follicles in advanced stages of degeneration are 

 often very irregular in form. 



The interfollicular (interstitial) epithelial cells (shown in fig- 

 ures 7 and 8), appear to undergo changes very similar to those 

 in the epithelium of adjacent follicles. 



The interstitial connective tissue or stroma of the thyroid in 

 maintenance rats may be nearly normal in amount and structure 

 (as in figure 7), but is frequently increased. This increase is 

 apparently due to an infiltration of clear ground-substance, which 

 in extreme cases gives a very pronounced swollen, 'water-logged' 

 appearance (figs. 5, 8). It is evident that in such a case the 

 weight of the gland might remain normal, even with a marked 

 atrophy of the parenchyma. The fibers adjacent to the follicles 

 may form a denser layer, resembling a basement membrane (fig. 

 S). The nuclei of the connective tissue cells become shrunken 

 and pycnotic. The vessels may appear nearly normal, although 

 degenerated areas sometimes appear hyperemic. 



c. Structure of the thyroid gland in adult rats after acute or chronic 



inanition 



In 6 adult rats whose thyroid was studied the body weight had 

 been reduced 29 to 38 per cent by acute inanition (water but 

 no food) for 8 to 11 days; and in 3 adults the amount of food had 

 been reduced so there was a gi'adual loss of 33 to 37 per cent in 

 body weight during the chronic inanition pei'iod of 5 weeks. 

 The thyroid gland averaged about 0.039 g. (0.24 per cent of the 

 net body weight) in both series, which (compared with controls) 



