IXAXITIOX OF THYHOII) I X RATS 



317 



normal height (8-10 inicra) at correspoiuUiig age. The average 

 height in the maintenance rats is about (5 to 7 mici-a. Since the 



Fig. 8 A })orti()u of the same thyroid jihind shown in figure 5 (rat No. S 5.10, 

 maintenance from 21 to 67 days of age), magnified to show details of histological 

 structure. This represents the hj-perchromatic (various stages of karyopycno- 

 sis) type of structure, w^hich is tyi)ical. Follicular cells usually greatly reduced 

 in size. Cytoplasm mucli reduced in amount and markedly vacuolated ('hy- 

 dropic degeneration" ). Colloid varialile in appearance. InterfoUicular stroma 

 relatively much increased in volume, due to infiltration of clear ground sub- 

 stance. (X 750.) 



