RELATION OF lODIN TO THYROID 401 



flour, no mention will be made here. This phase of the work 

 together with certain histological data gathered by examination of 

 normal and thyroidectomized iodine-fed larv^ae, will be the 

 subject-matter of part II of this paper. The results obtained 

 with feeding normal larvae potassium iodine will be discussed 

 first. 



OBSERVATIONS 

 I. Experiments with feeding potassium iodide to 7iormal tadpoles 



The tadpoles were first fed potassium iodide and flour when 

 they averaged 10 mm. in length; none of the animals showed 

 indications of limb buds. April 11th, eight days after the 

 first administation of potassium iodide, the animals were 

 measured and examined with a microscope for limb buds. At 

 this time some of the larvae appeared somewhat emaciated and 

 about one-fourth of the animals had hind limb buds, though the 

 buds were small. The controls were somewhat larger than the 

 experimental larvae, but no limb buds were found. Table 1 

 gives the total length of twenty of the larvae from each culture, 

 in millimeters and indicates those animals with limb buds. 



April 18th. When examined on this date the potassium- 

 iodide-fed animals were lighter in color than their controls but 

 of about the same size. All of the experimental animals had 

 hind limb buds whereas none of the controls had developed 

 them (table 2), The emaciated appearance of the larvae, 

 noted at the previous examination, had disappeared, 



April 26th. The potassium-iodide-fed larvae had by this time 

 outgrown their controls and were considerably lighter in color. 

 All of the experimental animals had well-developed hind limbs 

 showing differentiation into the two primary divisions with toe 

 points. Only three of the controls had limb buds, none showed 

 any differentiation of parts. The difference between the two 

 cultures of larvae in regard to limb development was striking 

 (table 3). 



May 6th. The animals fed on the iodine compound were now 

 distinctly larger than the algae-fed larvae. The light color of 

 /these animals was marked. Their limbs were well developed — 



