THE PAEATHYKOID GLANDS 513 



the parathyroid glandules, had been unintentionally left behind and the 

 operation was incomplete. At this period Gley held the opinion that the 

 parathyroids represented embryonic thyroid tissue, which undergoes 

 hypertrophy and develops into functionally active thyroid after that gland 

 has been removed ; in other words, potentially embryonic thyroids. In this 

 he was probably influenced by the description of these organs given by 

 Baber (1880). 



These important researches of Gley, begun in 1891, were continued by 

 him and his pupils for a number of years, and the results are embodied in 

 a series of papers published, for the most part, in the Comptes Kendues 

 de la Societe de Biologic, from 1891 to 1897 and later. Soon after his 

 first publication many other workers were attracted by this fascinating 

 problem and our knowledge of the subject became greatly extended. Gley's 

 ideas on the importance of the parathyroids were supported by some and 

 denied by others, 



Moussu (a) (1892) repeated the experiments of Gley on the rabbit, 

 and of eleven adults so treated none succumbed. Considering these nega- 

 tive results,- this author refused, at that time, to recognize the important 

 role assigned to the parathyroids by Gley. 



Hofmeister (&) (1894) did not admit that the parathyroids left in situ 

 at the operation either increase in size or become modified in structure in 

 any way. In young rabbits, he concluded, extirpation of the thyroids alone 

 gives rise to typical cachexia, which runs a, chronic course, while simul- 

 taneous ablation of the parathyroids leads to fatal tetany. 



This transformation of the parathyroids left behind into thyroid 

 tissue was also denied by Vassale and General!, and later (1895) Gley 

 himself, in association with Nicolas, on further experimentation, failed to 

 find any such change. 



Discovery of the Internal Parathyroids and Subsequent Experimen- 

 tation. The next important advance was made by Kohn (a) in 1895 when 

 he discovered that in addition to the glandules described by Sandstrom, 

 Gley, and others, there were two additional and similar bodies embedded in 

 the substance of the thyroid lobes. These are now usually known as the 

 internal parathyroids. According to Kohn, every animal is provided with 

 four parathyroids, arranged in two pairs, an internal pair imbedded in the 

 substance of the thyroid, and an external pair, situated at some distance 

 from the thyroid in the herbivora, but in the carnivora lying on the surface 

 of that gland and usually within its capsule. This observer insisted that 

 the parathyroids are organs anatomically separate and functionally distinct 

 from the thyroid. Later, as the result of a more extensive investigation, 

 he was confirmed in his original opinion and demonstrated the separate 

 embryological origin of the thyroids and parathyroids. 



The Italian observers, Vassale and General! (c) (1900) were the first, 

 from the experimental side, to avail themselves of this additional anatom- 



