

•« •' 



•r^-^yvi^ 



Fig. 4-7. Camera lucida drawings of sections of thyroid glands from 

 the guinea pig, Cavia, rapidly frozen-dried at intervals after inject- 

 ing standard doses of thyroid stimulating hormone, TSH ( < 2150). 

 (a and b) after half an hour and (c) after 6 hr from the time of inject- 

 ion, to show gradual increase in cell-size and accumulation of droplets 

 near the inner surface of the cells, through which some are passing 

 into the intrafollicular store of colloid above ; (d and e) a later stage 

 with increase in cell height and a reversal of the direction of cell 

 activity. Colloid is being reabsorbed from the store as clear drop- 

 lets, and secreted towards the surface of the cell next to the blood 

 capillaries below (from de Robertis, 1949). 



