24 The Endocrine Organs 



The most satisfactory explanation of the nervous results of the removal 

 of the parathyroids is the assumption that they yield to the blood a special 

 autacoid presumably of a chalonic or restraining nature which tends to 

 prevent over-excitation or discharge of nerve-cells. It has been suggested 

 that the over-excitation, since it occurs most markedly in carnivora, is 

 induced by products of protein metabolism. Some species exhibit no 

 symptoms whatever at least when the operation is performed on the 

 adult. Horsley stated that this is the case Avith birds and rabbits ; but, 

 according to Gley, the latter are affected if care is taken to find and remove 

 all parathyroids. Doyon and Jouty obtained typical tetany in hens which 

 had been parathyroidectomised. Vincent and Jolly found that rats and 

 guinea-pigs do not seem to suffer from removal of their parathyroids, but 

 Christian! and Erdheim both readily obtained tetania parathyreopriva in 

 rats, although in them it takes much longer to produce a fatal result than 

 in most animals ; and Pfeiffer and Meyer obtained it in mice. According 

 to Vincent and Jolly, badgers are totally unaffected by complete removal 

 of both thyroids and parathyroids. 



It is possible that insufficient attention has been paid to age by many 

 who have experimented on the subject. For it is certain that with the 

 exception of puppies, which are less susceptible than adult dogs young 

 animals are much more susceptible both to thyroidectomy and to para- 

 thyroidectomy than adults. This is strikingly exemplified in experiments 

 by v. Eiselsberg and by Sutherland Simpson on sheep and lambs. They 

 found, as had been done by others, that sheep show no symptoms what- 

 ever as the result of complete removal of thyroids and parathyroids, 

 while lambs exhibit both symptoms of tetany and arrest of development 

 with supervention of cretinism (fig. 17). Adult goats, on the other hand, 

 may exhibit well-marked tetania parathyreopriva. In monkeys this 

 condition has often been missed, but it occurs if the removal of para- 

 thyroids is complete. 



As already mentioned, Halpenny and Thompson describe changes in the 

 thyroid (of dogs) following parathyroidectomy (fig. 16) which resemble the 

 changes met with in exophthalmic goitre in man (see p. 37), and are 

 usually interpreted to mean increased activity of the gland. If this inter- 

 pretation is correct, we must regard the parathyroids as exercising an 

 inhibitory influence upon the thyroid, and some at least of the symptoms 

 of parathyroidectomy as due to the removal of this restraining influence. 

 Rudinger has upheld the view that there is reciprocal antagonism between 

 thyroid and parathyroids. 



Various clinical symptoms are associated with pathological changes 

 in the parathyroids, and have been referred (1) to atrophy or diminished 

 secretion (hypo-parathyroidism), (2) to enlargement or increased activity 

 (hyper-parathyroidism), (3) to altered secretion (dys-parathyroidism). 

 To the first condition must be ascribed manifestations resembling those of 

 tetania parathyreopriva. These occur under various circumstances, e.g. 



