THE PITUITARY AND THE THYROID 



have since been repeatedly confirmed. There is usually only 

 a moderate hypertrophy of the thyroid such as a 50 per cent 

 increase in weight; Loeb and Friedman (1931), however, 

 have reported that the thyroid lobes of treated animals may 

 weigh nearly three times as much as those of control animals." 

 Microscopically the colloid-containing vesicles are reduced in 

 size presumably because of colloid absorption and discharge 

 through the acinous cells. The remaining colloid is more 

 vacuolated and stains less well than that of control thyroid 

 tissue. The acinous cells hypertrophy and assume a cuboidal 

 or columnar appearance in contrast to the flatter normal 

 cells. Granules appear in the acinous cells, particularly in the 

 lumen poles. Proliferative activity in the acinous cells is 

 apparently great inasmuch as the number of mitoses is mark- 

 edly increased. Indeed, Watrin and Florentin (1932) regard- 

 ed the increase in the number of mitoses as the best criterion 

 of thyroid stimulation. Heyl (1933) believed that the other 

 effects could be graded in six stages. The histologic appear- 

 ance of the thyroids of littermate guinea pigs, one of which 

 had received anterior pituitary, is shown in Figure 48. 



If injections of anterior-lobe extract are continued, the 

 microscopic appearance of the thyroid indicates that different 

 parts of the gland are in stages of activity ranging from rest 

 to active secretion (xAron, 1930). Loeb and Friedman (1931) 

 secured the maximum effects from six or seven injections, 

 given once daily, into young guinea pigs. They found that if 

 injections were continued 2 months or longer the microscopic 

 evidences of stimulation of the thyroid disappeared except 



Loeb's laboratory (effective by mouth even after thyroidectomy, contain 10-50 

 times as much organic iodine as ordinary anterior-lobe powder, prevent compensa- 

 tory hypertrophy, etc.). 



" According to Heyl (1934), thyroid hypertrophy is due to a separate anterior- 

 lobe principle which produces this effect only by acting synergistically with the 

 principle causing histologic signs of thyroid stimulation. 



[261I 



