308 INFLUENCE OF THYMUS 



titles, in other parts of the thymus, in normal food, and perhaps in the 

 water of certain localities where unsuccessful experiments on thymus 

 feeding have been carried out. 



If the preventive influence, which the th3mius exhibits in some of 

 the larvag, is due to the presence of some specific metamorphosis- 

 inhibiting substance, metamorphosis evidently should be prevented 

 by the thymus even if normal food is added to the thymus diet. 

 This is the case, for instance, with the metamorphosis-producing 

 substance of the thyroid gland. Lenhart^ has shown that if a cer- 

 tain amount of the active substance of the thyroid, able to produce 

 accelerated differentiation and not large enough to result in death 

 from emaciation before differentiation can take place, is introduced 

 into the organism, differentiation will be accelerated and at a definite 

 rate, whether the tadpoles are fed only on thyroid or whether some 

 other food (liver) is added to the glandular diet. In fact, it seems, 

 from all experiments so far performed with thyroid, that it is of no 

 importance what food the larvae receive; the addition of only a 

 minute quantity of thyroid substance causes metamorphosis at an 

 accelerated rate. We found the same to be true for the larvae of 

 salamanders. Young (5 weeks old) larvae of Amhystoma opacum 

 which were fed on earthworms, were placed in a 0.02 per cent solu- 

 tion of iodothyrin; in spite of the earthworm diet and of the small 

 quantity of thyroid substance used (Bayer's iodothyrin), all larvae 

 metamorphosed from 8 to 9 days after the commencement of the 

 thyroid treatment, while the controls needed 7 to 8 weeks more to 

 metamorphose. The thymus itself contains a specific substance which 

 is highly toxic and produces tetany in the larvae of Amhystoma macu- 

 latum and opacum as described in a former article.' The action of 

 this substance as regards its constancy is quite similar to the action 

 of the metamorphosis-producing substance of the thyroid and very 

 unlike the metamorphosis-inhibiting action of the thymus. No mat- 

 ter what food is added to the thymus diet larvae fed on thymus always 

 had tetany. And like the thyroid substance, the tetany toxin of the 

 thymus is also characterized by the constancy of its action; it pro- 

 duces tetany in each individual. 



^Lenhart, C. H., /. Exp. Med., 1915, xxii, 739. 



