408 W. W. SWINGLE 



hormone into the network of capillaries surrounding the gland in 

 sufficient quantities to induce transformation, we are led to the 

 conclusion that in the last analysis the crux of "the problem is 

 defective stimulation (perhaps inhibition) of the gland by that 

 portion of the animal's nervous system responsible for the flow 

 of secretion under normal conditions. 



How else can one reduce to harmony the multiplicity of factors 

 that have been invoked to explain axolotl metamorphosis, save 

 by reducing them all to a common factor: i.e., agents which pro- 

 duce their effect by subjecting the organism to more or less violent 

 changes of the environment thus acting as a constant nervous 

 stimulant? For example, a few of the agents (aside from thjn^oid 

 or iodine feeding)^ that have served to initiate axolotl metamor- 

 phosis are : sudden changes in food supply, drying of swamps or 

 pools in which the animals live, changes in the temperature of the 

 water (Shufeldt, '85) ; forcing the animals to breathe air, insuf- 

 ficiently aerated water (Chauvin, '75, '77); administration of 

 sahcylic acid (Kaufman, '18); shifting of the animal from its 

 normal habitat to other districts, such as from New Mexico to 

 New Haven. 



A glance at this list of factors indicates that their varied nature 

 alone negatives the idea that any one of them can be the real 

 causative factor in axolotl metamorphosis. However, all can be 

 classed as shocks to the organism, and it may possibly be that 

 such more or less constant excitation may bring about nervous 

 stimulation to the thyroid sufficient to overcome the inhibiting 

 influence and release the stored secretion, thus initiating meta- 

 morphosis. The nature of the inhibiting factor is of course the 

 crux of the problem, and in the last analysis is probably of endo- 

 crine origin acting through the intermediation of the nervous 



^ Apropos of Uhlenhuth's claims that iodine has nothing to do with axolotl 

 metamorphosis, the recent papers of Jensen and Hirschler are of interest. Jensen 

 (Compt. Rend. Soc. de Biol., T. 85, 1921) metamorphosed axolotls by injections of 

 iodocasein, iodoserumglobulin, and iodoserumalbumin. Also by feeding with an 

 organic iodine compound — iodo-thyrosin. Hirschler (Arch. Entw. Mech., 1922) 

 metamorphosed axolotls and anuran tadpoles bj^ feeding elemental iodine in 

 various forms. These investigators worked on strains of axolotls which do not 

 spontaneously transform. 



