Antagonism between Thymus and Parathyroid. 71 



place, tetany develops as soon as a certain amount of the tetany 

 toxin has been accumulated in the organism (Table I, Series XXV, 

 1 91 8). The time required for accumulation of that amount is 

 far shorter than the intervals in the first two series. It is, however, 

 longer than in the fourth series, because the animals of series 

 XXV. had been fed twice as long on normal diet and besides had 

 almost twice as much time to grow before the thymus diet was 

 started, and larger animals need more of the tetany toxin than 

 small ones to develop tetany. 



Hence, it is evident that the amphibian thymus gland manu- 

 factures a secretion similar to that of the mammalian thymus, 

 and that the amphibian organism even in the absence of para- 

 thyroid glands can antagonize a certain amount of the toxin, be it 

 excreted from its own thymus glands or introduced by thymus 

 feeding before the animal's own thymus glands have developed; 

 but excretion of their own thymus glands and thymus feeding at 

 the same time lead finally to the accumulation of an excess amount 

 of the tetany toxin, of which the parathyroidless organism of the 

 salamander larva cannot dispose, and consequently tetany results. 



But when the thymus-fed larvae metamorphose, the tetanic 

 convulsions stop and never recur after metamorphosis has taken 

 place, even if the animals are continued on an exclusive thymus 

 diet. Since during metamorphosis the animals develop their 

 parathyroids, it was concluded that the parathyroid glands now 

 serve to antagonize the tetany toxin and that the parathyroidal 

 mechanism is more efficient than the one existing in the larvae since 

 the parathryoids are able to antagonize not only the tetany toxin 

 excreted by the animal's own thymus glands but also the toxin 

 introduced by the thymus died. 



But it might be that after the tetany toxin has acted for a 

 certain length of time upon the central nervous system and all 

 the motor nerve cells have been destroyed, no further muscular 

 contraction would be possible, and that possibly the time of com- 

 plete destruction of the motor nerve cells coincides with the period 

 of metamorphosis. 



If this were true, one would expect that when a normal sala- 

 mander is fed on thymus shortly after metamorphosis, tetanic 

 convulsions would be produced after about four weeks of thymus 



