/. Endocrine factors in development 



40. EFFECT OF THYROID AND OF 

 IODINE ON AMPHIBIAN METAMORPHOSIS 



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

 stituent (iodine), to metamorphic changes in the vVmphibia. 



MATERIALS: 



Biological: Hatched tadpoles of Rana, Bufo, or Hyla 



Neotonous Urodele larvae (Necturus, Axolotl, etc. ) 



Technical : Thyroid tablets (Armour h. Company) 



Thyroxin crystals (Hoffman-La Roche Company) 



Freshly dissected thyroid glands (frog, rat, sheep, 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 tad- 

 poles. 



3. 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 tadpoles 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 con- 

 trol 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 be- 

 ginning of the experiment. 



Procedure : 



PREPARATION OF EXPERIMENTAL MEDIA 



Thyroxin: Dissolve 10 mgm. of crystalline thyroxin in 5 cc. of 1% NaOH (it is sol- 

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

 be a 1/100, 000 concentration of thyroxin and may be kept in the refrigerator almost 

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

 tions of experimental media are made. 



Thyroid Tablets : Dissolve five 2-grain tablets in about 5 cc. of distilled water, us- 

 ing a mortar and pestle. Add an equivalent amount (in weight) of whole wheat flour, 

 and grind together thoroughly. With a spatula, spread the paste thinly 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. 



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



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