INANITION OF THYROID IN RATS 319 



111 the larger peripheral follicles, in whieli th(> e))itlieliuiii is iioi'- 

 mally flattened, the change is usually not so apparent in the 

 maintenance rats. Even here, however, there is a further flat- 

 tening of the epithelial cells, which frequently present an endo- 

 thelial-like appearance, with a height of onl}- 2 or 3 micra. 



The cytoplasm of the thyroid epithelium in the maintenaiic(^ 

 rats has undergone marked changes (figs. 7, 8, 9). In compari- 

 son with the normal (fig. 2) , it appears that the amount has been 

 greatly reduced, the decrease in the size of the cell being due 

 very largely to loss of cyoplasm. 



The cytoplasm is also greatly changed in structure, having ap- 

 parently undergone a 'hydropic degeneration.' The normal 

 granular appearance of the cells (fig. 2) has been replaced very 

 largely by a distinct reticular appearance (figs. 7 and 8). This 

 appears to be due to a coarse vacuolization of the cytoplasm, a 

 condition rarely found in the normal gland. The vacuolization 

 is especially marked in the few larger cells which have retained 

 more cytoplasm than usual. Occasionally the vacuoles coalesce 

 to form perfectly clear perinuclear areas (see upper part of fig. 

 8) . These clear areas and vacuoles probably represent a watery 

 fluid replacing the normal granular substance, which has been 

 removed and consumed as a result of the inanition. 



Where the cytoplasm is very greatly reduced in amount (as in 

 the larger peripheral follicles), the vacuoles may be finer or ab- 

 sent, and the cytoplasm here presents a denser, more deeply- 

 staining (eosinophile), often homogeneous appearance ('colloid' 

 type). In the case of cells in advanced stages of degeneration 

 (which appear much more frequent and more pronounced than 

 in the normal at this age), the cytoplasm is more or less disin- 

 tegrated and extremely varied in appearance (fig. 9). It usually 

 presents an irregular, deeply-staining (eosinophile), coarsely 

 granular mass, which, especially in the desquamated cells, be- 

 comes fragmented and is gradually absorbed, frequently leaving 

 behind the naked, pycnotic nuclei (fig. 9). The cell walls are 

 often distinct in the less modified epithelium, but usually indis- 

 tinct or lost in the cells markedly degenerated. 



