EDUARD UHLENHUTH 29 



Correspondingly the epithelial character of the glands is lost; this 

 finds its expression also in the fact that pigment granules have dis- 

 appeared altogether. In addition a considerable number of mitoses 

 may be found, which mostly seem to be cell divisions of the newly 

 arrived elements. Of particular importance is the fact that in one of 

 the glands of the fifth pair, which I found to be frequently ahead of 

 the third and fourth pairs in development, the cell plasma of a number 

 of cells stains pink, and here one nucleus which also is stained pinkish 

 exhibits a swollen appearance, characters which are ascribed by Maxi- 

 mow to the formation of the medulla of the thymus. 



The thymus glands of the pretetanic larvae are therefore mere 

 accumulations of epithelial cells and do not possess any structures to 

 indicate that they would be capable of exerting any of the functions 

 of a thymus, while in the tetanic larva at least some of the glands 

 resemble a true thymus and probably have commenced to behave as 

 such with regard to function. From these observations we may con- 

 clude that the thymus feeding does not begin to call forth tetany in 

 salamander larvae until the thymus glands of the larvae themselves are 

 able to secrete. This suggests that tetany is the effect of the combined 

 action of the secretion of certain substances by the thymus glands of 

 the larvae and 'of substances introduced into the larva by feeding it 

 with the thymus gland from other animals. 



Prevention of Tetany by the Parathyroids. 



It is well known that salamander larvae do not possess parathyroids ; 

 these glands develop during metamorphosis. Though the end of the 

 tetanic period coincides approximately with the development of the 

 parathyroid glands, yet larvae which had ceased to show convulsions 

 for some time apparently possessed no parathyroids when examined 

 histologically. It is, however, possible that in spite of this in such 

 larvae certain processes had commenced which would soon have led to 

 the formation of these glands and that these processes were already 

 able to check tetany. 



A connection between the development of the parathyroids and the 

 cessation of tetany seems probable on account of the fact that tetany 



