^ THYROID AND IODINE AND METAMORPHOSIS 



food three times per week. If available, separate the tadpoles ao that there are 

 no more than 100 per enamel pan and they will grow faster. 



2. When the hind limb buds have attained a length of about 1 mm., select as many as 

 are available at exactly the same stage of development. Place 5 such tadpoles in 

 each finger bowl containing 50 cc. of Standard Solution or Spring Water. (If 

 available, the 12 inch crystallizing dishes may be used with 25 such tadpoles.) 



In any case the stage of development, volume of medium, and size of container must 

 be identical for all groups of tadpoles. 



3. Treat the experimental animals as follows (the controls receiving the spinach diet 

 only while the experimentals receive, in addition, the following). 



THYROXIN : Place tadpoles in various concentrations for 1 week . Do not suspend 

 normal feeding. 



a. Concentration of l/l,000,000 



b. Concentration of l/l0,000,000 



c. Concentration of l/l00,000,000 



Doses of 1/500,000,000 have been known to accelerate development. 



THYEOID TABLETS : Add approximately 50 mgm. of thyroid-wheat mixture per day 



per tadpole, for a period of one week. Do not suspend normal feed- 

 ing, and change the culture medium daily just before adding thyroid. 



lODIME: Add concentration and normal food but add no further iodine unless 

 the medium is changed. 



a. Concentration of l/500,000 for 7 and for Ih days. 



b. Concentration of l/l,000,000 for 7 and for l4 days. 



FRESH MAMMALIAN THYBOID : This experiment can have only qualitative significance 

 because it is difficult to control the dose of the thyroid colloid 

 expelled from the living (fresh) glands or the amount ingested by 

 each of the tadpoles. It will be significant, however, if the stu- 

 dent can demonstrate any acceleration of amphibian metamorphosis by 

 the use of mammalian thyroid gland tissue or colloid. It is possible 

 simply to squeeze fresh thyroid glands directly into the experimental 

 dishes, thus liberating some of the colloid to be Ingested. 



If bullfrog tadpoles are available, their thyroids may be used 

 in the same manner. Such tadpoles can also be used as test animals, 

 providing they are second -year tadpoles and have begun the develop- 

 ment of their hind limbs. 



h. Neotony is a condition of permanent larval state, during which the forms can re- 

 produce. Examples are Necturus and the Mexican Axolotl. Such forms can be caused 

 to complete their arrested development, and metamorphose, by treating them with 

 the thyroid hormone or iodine. If available, attempt to get rid of the otherwise 

 permanent external gills of such forms by treating them with thyroxin. Evan 

 A. punctatum and A. tirgunum may be hastened through metamorphosis by thyroid 

 treatment. 



OBSERVATIONS AND TABULATION OF DATA: 



There is high mortality in this type of an experiment. 



Mount some millimeter graph paper on the underside of some flat-bottomed Petri dishes 

 to use as a guide in determining the size changes in tadpoles. The important criteria 

 are: 



a. Hind limb length 



b. Total length, i.e., from snout to tip of tail 



c. Body length, i.e., from snout to base of tail 



