62 



R. R. BENSLEY 



high. Like the preceding series the content of colloid is high, 

 and the cells of all three glands contain small globules of colloid. 

 Mitoses were abundant in all three glands, but most numerous 

 in the glands from animal number seven in which the hyperplasia 

 was highest, and the reaction to the iodides, as indicated by the 

 content of colloid, lowest. In this gland mitoses were so abun- 

 dant that often three or four might be seen in a single field of the 

 3 mm. aprochromatic objective. 



This series of experiments shows that, given the conditions 

 which by themselves produce hyperplasia, iodides are not able 

 per se to inhibit the hyperplasia, and that the hyperplasia is not 

 due to deficiency of iodine. This result, at first sight contrary 

 to Marine's conclusions, is not really so, since Marine has recog- 

 nised that in the thyroid hyperplasia of the trout there are 

 periods of greater and less susceptibility to iodine administration, 

 and that the milder degrees react more promptly to iodine than 

 the more severe ones. It may be presumed that mitosis and se- 

 cretion are to a certain degree mutually exclusive, and that, 

 therefore, the susceptibility of the gland to iodine is inversely 

 proportional to the rate of hyperplasia. In the same way one 

 might assume that, to the extent to which normal secretion could 

 be maintained hyperplasia would be prevented, and thus iodine 

 given at suitable times would prevent hyperplasia. In the 

 present series, however, the impulse to hyperplasia is too strong 

 for the iodine to overcome. 



Table 4 represents the results in eight animals kept for a 

 period of three weeks on a diet nearly sufficient to maintain 

 constant weight. In one group, consisting of numbers 9, 13 and 



c 



