EFFECT OF IODINE ON LARVAE OF SALAMANDERS. 151 



suits of the present experiments. Bayer's iodothyrin, according 

 to Bayer's " Materia Medica " and according to Baumann's own 

 description of this substance, contains 0.3 mgm. iod'ine per I gm. 

 of substance. Consequently a dosis of o.i gm. of iodothyrin, 

 which causes very rapid metamorphosis of the axolotl larvae, con- 

 tains 0.03 mgm. iodine per 1,000 c.c. of water. The weakest so- 

 lution of inorganic iodine employed 'in the iodine experiment (5 

 drops of a M/2O iodine solution per 1,000 c.c. water) contained 

 approximately i.o mgm. of iodine per i.ooo c.c. of water (i drop 

 being equal to about 0.2 mgm. of iodine), while the strongest solu- 

 tion contained even 2.6 mgm. iodine per 1,000 c.c. \vater. In ad- 

 dition to these quantities of inorganic iodine the larvae of the 

 iodine series received, directly per mouth, a total amount of 25 

 iodine crystals which equals approximately 40 mgm. of 'iodine, 

 the average weight of one crystal being 1.6 mgm. Yet these 

 quantities of inorganic iodine did not cause metamorphosis, al- 

 though they were greatly in excess over the quantity of iodine 

 contained in an effective dosis of iodothyrin. It is obvious that 

 it is not the quantity of iodine contained in the iodothyrin, which 

 produces the effectiveness of the latter substance. 



Lenhart's experiments 10 showed that the effectiveness of 

 thyroid; gland in the amphibian metamorphosis of tadpoles in- 

 creases with an increasing amount of iodine. These experiments 

 are frequently quoted to demonstrate quantitatively that the 

 active substance of the thyroid hormone in the amphibian meta- 

 morphosis is iodine. In the light of the present experiments this 

 interpretation of Lenhart's experiments seems untenable. As 

 pointed out in the introduction of this article, it is probable that 

 the inorganic iodine does not produce the metamorphosis of tad- 

 poles in its inorganic form, but after the thyroid apparatus has 

 elaborated from it the thyroid hormone. Therefore Lenhart's ex- 

 periments may be simply the expression of the fact that the tad- 

 pole thyroid, as claimed by Swingle 11 elaborates more hormone if 

 more iodine is available. Moreover it is very probable that in 

 Lenhart's experiments an increased amount of iodine contained 



9 Baumann, E., and Roos, E., Zeitschr. f. physiol. Clicin., 1895-96, 481-493. 



10 Lenhart, C. H., /. Exper. Med., 1915, xxii, 739-746. 



11 Swingle, W. W., /. Exper. Zool., 1919, xxvii, 417-425. 



