INANITION OF THYROID IN RAT8 311 



The colloid (fig. 2) appears typical in form though somewhat 

 variable in staining reactions. In some cases it fills the follicu- 

 lar cavity completely, in other cases it is retracted somewhat 

 with either smooth or serrated margin. This retraction is prob- 

 ably an artefact in most cases, due to shrinkage jDroduced by 

 the reagents used. But I cannot agree with those investigators 

 who explain the vacuoles (some of which are shown in figure 2) 

 in a similar manner. These vacuoles are usually small (4 micra 

 or less) and spherical in form, and are most frequent near the 

 surface of the colloid. Occasionally they are found in intimate 

 relation with the adjacent cells, from which they are apparently 

 extruded, as shown in the follicle on the right in figure 2. They 

 are probably connected in some way with the process of colloid 

 formation, as described by Anderson ('94) and Mliller ('96). 

 Desquamated epithelial cells, which sometimes dissolve leaving 

 clear vacuoles in -the colloid in older rats, are extremely rare at 

 this stage. 



A variable amount of interfollicular epithelium appears, which 

 cannot be distinguished from tangential sections of follicles, ex- 

 cept in serial sections. In structure, these interstitial epithelial 

 cells are similar to those of the follicles. A few appear in the 

 lower part of figure 2. 



The interfollicular connective tissue forms a delicate fibrous 

 stroma (fig. 2), relatively small in amount, but containing a 

 rich capillary plexus of blood-vessels. The nuclei visible are 

 mostly of capillary endothelium. They are elongated or flat- 

 tened in form, and stain somew^hat deeply. 



At 10 weeks (the age when the inanition experiments ended in 

 most of the younger rats) the thyroid gland has normally under- 

 gone but slight changes, the structure being essentially the same 

 as that just described at three weeks. Therefore no detailed 

 figures are considei-ed necessary. A photograph with low mag- 

 nification is shown in figure 3, representing a cross section of one 

 lateral lobe. The follicles have increased somewhat in size, 

 the maximum diameter now reaching about 100 micra. The 

 larger follicles are more frequent, and are sometimes rather uni- 

 formly distributed, as shown in figure 3, though very frequently 



