THE THYROID APPARATUS 51 



purposely left in situ. It seems, however, highly improbable 

 that accessory glands should be present in just those cases which 

 have been treated by thyroid extract, especially as such super- 

 numerary bodies are extremly rare in certain species, such as 

 the cat. But even allowing that there is some foundation for 

 Vassale's assumption, a certain measure of efficacy must be 

 granted to the thyroid extract, for it is undoubtedly the agent 

 by which the animals are carried through a phase of disease in 

 which they would otherwise certainly perish. 



With so little knowledge at our disposal we are not in a 

 position to give any definite explanation of the effects of the 

 thyroid preparations in tetany, but I do not think this should 

 prevent us from drawing from the analogy of experimental 

 pathology a conclusion which is of the utmost importance to man. 

 It is, that treatment with thyroid gland should always be tried 

 where the extirpation of goitre is followed by symptoms of 

 tetany. By this means time is gained, during which the para- 

 thyroids and any accessory parathyroids are enabled to attain 

 the full measure of their functional activity; or a substitute for 

 such activity may be provided by means of transplantation. 



THE RELATIONSHIP BETWEEN THE THYROID AND 

 PARATHYROID GLANDS. 



Gley's view that the parathyroids are embryonal organs 

 which, after the removal of the thyroid gland, assume the function 

 of the principal organ, and thereupon acquire the structural 

 characteristics of thyroid tissue, has not been endorsed by later 

 authors. His discovery that, after the removal of the thyroid 

 and inner parathyroids, the external parathyroids became 

 hypertrophied, is confirmed by many, but no proof is forthcoming 

 of a histological structural transformation of parathyroid tissue 

 into thyroid tissue. Gley himself, in combination with Nicolas, 

 has recently repeated his experiments, and has been compelled to 

 abandon his former view. Vincent and Jolly describe such 

 structural transformation of the parathyroids in cats, but they 

 are alone in their experience. 



Quite recently- Vincent, Halpenny and Thompson found that 

 the external parathyroids of a dog from which the thyroid and 

 internal parathyroids had been removed eighty-three days 

 previously, were hypertrophied and changed in such a manner 

 that it was difficult to distinguish them from thyroid tissue. In 

 addition to parathyroid tissue composed of compact rows of cells, 

 the drawings of these organs show numerous irregular vesicles, 

 lined with a single layer of epithelial cells, in part empty and 

 in part filled with colloid. The histological picture of these 

 glands has a strong resemblance to that of a thyroid which the 



