232 W. W. SWINGLE. 



and the globulin was injected in powdered form. This method 

 because of the ease with which it could be performed was also 

 utilized in the tyrosine experiments. Forced feeding of the ani- 

 mals with the various substances by means of a pipette thrust 

 down the oesophagus into the stomach, might have been as effec- 

 tive as injections, but the animals usually regurgitate some of 

 the material, at any rate this was found to be the case in an 

 earlier experiment where desiccated thyroid tissue was adminis- 

 tered by forced feeding. 



The pigment pattern characteristic of adult Amblystoma 

 tigrinum is not completely developed in axolotls until several 

 weeks following metamorphosis. 



Jensen ('21) metamorphosed axolotls (with intact thyroid 

 apparatus) by injections of iodized casein, iodoserumglobulin, 

 and iodoserumalbumin. He also removed the thyroid glands of 

 axolotls and attempted to metamorphose the larvae by injections 

 of iodized proteins but his animals died. He concluded that such 

 iodized proteins are highly toxic for thyroidless animals but not 

 for those possessing normal glands. In my own experiments the 

 axolotls withstood the injections of iodized amino-acid and 

 serumglobulin as well as those with pieces of the gland present. 

 There was nothing in the behavior of the animals to indicate that 

 iodized substances are more toxic for thyroidless axolotls than 

 for normal animals. Iodized substances are certainly not more 

 toxic for thyroidless anuran tadpoles than for normal larvae. 



In an earlier experiment than those recorded here three axolotls 

 were thyroidectomized and injected with large doses of iodotyro- 

 sine. The animals were kept in ordinary glass aquaria without 

 running water. All of the animals died within ten days following 

 injection. In later experiments the injected axolotls were kept 

 in large concrete tanks, filled to capacity and with fresh water 

 running constantly. None of the animals died. Intraperitoneal 

 injections of large doses of either iodotyrosine or iodoserum- 

 globulin has a marked depressing effect upon thyroidless axolotls; 

 the animals are sluggish, move about very little, refuse food, and 

 show indications of weakness for several days or even a week 

 following injection. 2 



2 A large axolotl was thyroidectomized and kept for eight months then twice 

 injected at eight day intervals with large amounts of iodized casein. Metamorphosis 

 resulted within twenty-nine days. 



