THE PAEATHYEOID GLANDS 519 



This detailed research led to conclusions at variance with the previously 

 accepted belief in the constancy of number of parathyroids in each species. 

 For example, in three specimens of the green monkey ( Cercopithecus calli- 

 trichus) examined, the parathyroids numbered one, one, and eight, respec- 

 tively. Although, in the majority of cases, only four are found, still the 

 parathyroids frequently vary in position and number in different species, 

 and in different members of the same species. Further, the existence of 

 parathyroid tissue in the thyroid, not isolated by connective tissue, was 

 found to be of much commoner occurrence than was anticipated. Forsyth 

 goes on to say that "intermediate types" (between thyroid and parathyroid 

 structurally) are readily found both in the thyroid and in accessory glands, 

 with the result that the identity of some bodies has often presented diffi- 

 culty. "Under these circumstances it might have appeared undesirable to 

 retain the two expressions thyroid and parathyroid; but, since the histo- 

 logical distinction between the two is widely recognized and is a convenient 

 one, it was found advantageous to employ both in the following descrip- 

 tions. The usage is not to be taken as an assent to the proposition that 

 there is functional difference between the thyroid and the so-called para- 

 thyroid glands." 



At this time, as we have seen, the great majority of workers agreed 

 with the teaching of Grley and of Vassale and Generali, viz., that removal 

 of all the parathyroids from an animal, even if the thyroids be left intact, 

 invariably leads in a few days to the death of the animal from acute 

 nervous symptoms commonly known as tetania parathyreopriva, while 

 extirpation of the thyroid alone gives rise to chronic symptoms analogous 

 to those of myxedema in man postoperative myxedema or cachexia 

 strumipriva. It was held that the two organs are distinct and independent 

 structurally, embryologically, and functionally, and, as regards vital im- 

 portance, the thyroid is secondary to the parathyroids. 



Investigations as to the Relationship between the Thyroid and Para- 

 thyroids. In 1904 Vincent and Jolly published the results of an extensive 

 investigation into the physiology of the thyroid and parathyroids. They 

 used cats, dogs, foxes, monkeys, rats, guinea pigs, and rabbits in their 

 first series, and monkeys, cats, dogs, prairie wolves, badgers and rats in 

 their second. In their operations they experienced considerable difficulty 

 in separating the two glands. These difficulties, mainly anatomical, they 

 say, had been understated by previous workers. In speaking of the re- 

 moval of the internal parathyroids, Vincent says: "When it is remem- 

 bered how vascular the thyroid tissue is, how slightly the parathyroid 

 differs from it in appearance to the naked eye, and how this difference, 

 slight as it is, entirely disappears when there is any bleeding, it will be 

 seen that the operation of digging out the internal parathyroid is one of 

 extreme delicacy. A further difficulty presents itself in the fact that there 

 is a nodule of thymus also imbedded in the thyroid lobe, frequently in 



