418 W. W. SWINGLE 



material taken from these earlier cultures consisted entirely of 

 Rana pipiens larvae. The remainder of the material was taken 

 from cultures of iodin-fed Bufo larvae. All animals used were 

 appropriately controlled with animals of the same age and 

 reared under the same environmental conditions. The iodin-fed 

 larvae were killed and preserved for microscopic examination 

 when they showed qiarked indications of hyperthyroidism. The 

 fixing fluid used was potassium-bichromate-acetic (Tellye- 

 snicky's). Only the lower jaw and heart region were preserved. 

 After washing thoroughly, the tissue was placed in toto in alum- 

 cochineal for thirty hours; washed in distilled water and run 

 up through the alcohols to absolute. The tissue was cleared 

 and kept in oil of wintergreen until ready for use. All measure- 

 ments recorded for the glands were made with an eye-piece 

 micrometer, Bausch & Lomb microscope, 16-mm. objective, 

 ocular 1 . The greatest length and width of the gland only were 

 measured. 



CULTURE I. IODIN-FED AND CONTROL LARVAE 



The animals of this culture averaged 10.5 mm. in length when 

 first started on the iodin diet; none of the animals revealed any 

 indications of limb buds. Thirteen days from the date of first 

 iodin administration all of the experimental animals showed 

 marked symptoms of hyperthyroidism, the indications of which 

 are characteristic in this species (Rana pipiens). All growth of 

 the larvae had ceased with the first iodin feeding, and from then 

 on had in many of the animals actually decreased, owing to tail 

 resorbtion ; the larvae were emaciated ; tail atrophy was apparent ; 

 movement sluggish; all iodin-fed animals had well-developed 

 hind limbs. The controls for this culture showed none of the 

 changes enumerated, but had increased considerably in size. 

 None of the controls had limb buds. 



Table 1 gives the length of the animals of both experimental 

 and control groups and indicates the condition of the limbs 

 thirteen days from the beginning of the experiment. Two sets 

 of controls were used for each iodin-fed culture, one set was 

 fed beef and large quantities of algae each day, the other set 



