j:duard uhlenhuth 31 



tetany when fed to the larvae of certain species of salamanders {Am- 

 by stoma opacum and Amhy stoma maculatum). As long as the larvae 

 have not developed their own thymus glands, they are able, by means 

 of some mechanism, to counterbalance the tetanic action of the 

 thymus substance introduced in their food. When, however, the 

 secretion from their own thymus glands is added to the thymus mate- 

 rial introduced with the food, this mechanism of preventing tetany 

 becomes inadequate and tetany ensues. In the larva of a third 

 species of salamander, Ambystoma tigrinum, this mechanism will 

 prevent tetany even when the larvae are fed on thymus. 



In mammals the parathyroids are known to prevent tetany and are 

 supposed either to absorb the tetany-producing substance and thus 

 prevent its action or to change it into another non-toxic substance. 

 It is at least probable that in the amphibians the parathyroids play 

 the same role. Larvae of anuran amphibians, which develop their 

 parathyroids soon after hatching, never show tetanic convulsions if 

 they are fed on thymus, but in certain species of salamanders, whose 

 parathyroids develop only during metamorphosis, the larvae inva- 

 riably have tetanic convulsions upon thymus feeding, while the meta- 

 morphosed animals never show tetany. 



But in addition to the parathyroids the salamanders must possess 

 still another mechanism which during the larval period inhibits the 

 production of tetany by the animal's own thymus glands. In the 

 larvae of Ambystoma opacum and Ambystoma maculatum this mech- 

 anism is sufficient only to prevent tetany from the animal's own 

 thymus, while in the larvae of Ambystoma tigrinum it is capable of pre- 

 venting tetany even when the larvae are fed with thymus. 



If the thymus is the organ by whose action tetany is produced, we 

 can understand why tetany in human beings occurs far more frequently 

 in children than in adults, since in the latter the thymus gland is 

 replaced, at least to a great extent, by connective tissue. The relation 

 of thymus to tetany may also possibly explain the occurrence of tetany 

 during pregnancy; while the parathyroids of the mother may be suffi- 

 cient to prevent tetany from her largely atrophied thymus, they may 

 not be sufficient to prevent tetany from the excess of thymus sub- 

 stance furnished by the fetus to the blood of the mother. 



