518 BIOCHEMISTRY: ABEL AND PINCOFFS 
The severity depends to a great extent on the temperature in which 
the animals are kept. In low temperature the acute tetany begins later 
and is of shorter duration than in high temperature In high tempera- 
ture some animals succumb from the attacks; those which survive 
metamorphosis never show a complete recovery. In low temperature 
recovery may be complete and the animals can Hve after metamor- 
phosis for many months and reach an age of at least fourteen months, 
even if they are kept on exclusive thymus diet after metamorphosis. 
It should be particularly emphasized that no matter in what tempera- 
ture the animals are kept, acute attacks cease a short time before meta- 
morphosis and never occur in metamorphosed animals. 
The symptoms of the attacks caused by thymus in the larvae of A. 
punctatum and A . opacum are the same as in the attacks observed in 
mammals after parathyroidectomy and the theory that they are caused 
by the same agent as Tetania thyreopriva suggests itself. 
It would seem then, that thymus contains the substances which cause 
tetany and excretes them intb the body, from which they are removed by 
the parathyroids. Extirpation of the latter would thus cause tetany. 
If this is true, we should expect that thymus-f ceding would produce 
tetany only in such species as have no parathyroids. In fact tetany 
in thymus-fed tadpoles has never been reported; these animals develop 
the parathyroids several days after hatching. The Salamander larvae 
however, have no parathyroids and the occurrence of tetany in thymus- 
fed larvae of that species corresponds with our expectations. 
Furthermore, according to such a theory, thymus-fed animals which 
suffer from tetany should become free from it as soon as they develop 
parathyroids. The Salamanders develop parathyroids when they go 
into metamorphosis, which is actually the time that acute tetany 
ceased in our larvae. 
Although many experiments must still be made to clear the entire 
problem — some of which are already in progress — for the present, the 
above theory might be valuable as a working hypothesis. 
