EFFECT OF THYROID AND OF IODINE 

 ON AMPHIBIAN METAMORPHOSIS* 



PURPOSE: To demonstrate the relationship of the thyroid hormone, or its major constituent 

 (iodine), to metamorphic changes in the Amphibia. 



MATERIALS : 



Biological : Hatched tadpoles of Eana, Bufo, or ^la 



Neotonous Urodele larvae (Necturus, Axolotl, etc.) 



Technical : Thyroid tablets (Armour & Company) 



Thyroxin crystals (Hoffman-La Boche Company) 



Freshly dissected thyroid glands (frog, rat, sheet, etc.) 



Iodine crystals dissolved in 95^ alcohol 



Millimeter ruled graph paper on underside of Petri dish (for measuring) 



METHOD: 



Precautions : 



1. The number of tadpoles per unit of volume per finger bowl must be the same for 

 all observations. The best ratio is 25 tadpoles per 50 cc. of medium in each 

 finger bowl. 



2. The medium for the experimental animals should be changed daily except where 

 thyroxin is used. The thyroid tablets or glands provide an excellent medium for 

 bacterial growth which, in itself, would eventually kill the tadpoles. 



5. Avoid overdosing or overfeeding, particularly of iodine or thyroid material. The 

 effect of thyroid is an acceleration of development which may be carried beyond 

 the tolerable limit and the badpoles will be literally "burned up". 



Controls: Since the treatment of the tadpoles involves feeding, a basic diet of boiled 



spinach (1 square inch per tadpole per day) should be provided for both the control 



and the experimental animals. The controls and the experimentals should be from the 



same batch of eggs, at exactly the same stage and size at the beginning of the ex- 

 periment. 



Procedure : 



PREPARATION OF EXPERIMENTAL MEDIA 



TfflTBOXIN : Dissolve 10 mgm. of crystalline thyroxin in 5 cc, of l<f> NaOH (it is 

 soluble only in alkaline media) and then add distilled water to make 1 liter. This 

 will be a l/lOO,000 concentration of thyroxin and may be kept in the refrigerator 

 almost indefinitely and may be considered the stock solution from which lower con- 

 centrations of experimental media are made. 



TEfROID TABLETS : Dissolve five 2-grain tablets in about 5 cc. of distilled 

 water, using a mortar and pestle. Add an equivalent amount (in weight) of whole 

 wheat flour, and grind together thoroughly. With a spatula, spread the paste thin- 

 ly onto clean lantern slide covers and allow it to dry. When dry, chip the mixture 

 off of the glass, powder and store it in stoppered bottles in the refrigerator. 



IODINE SOLUTIONS : Dissolve 0.1 gram of pure crystalline iodine in 5 cc. of 

 95^ alcohol, and then dilute to 1 liter with distilled water. This will provide a 

 concentration of l/lO,000 as a stock solution, which can be further diluted when 

 required for experimental uses. 



* The author acknowledges with appreciation, the help of Dr. S. A. D'Angelo in organizing 

 this exercise. 



-522- 



