METABOLISM, NUTRITION AND DIETETICS 487 



of the heart and partly to the dilatation of the vessels. 

 Neutral inorganic salts of iodine, such as sodium iodide, 

 have the opposite effect, paralyzing the vagus and depressor 

 fibres, increasing the excitability of the augmentors and 

 vaso-constrictors, and causing in both ways an increase of 

 blood-pressure. lodothyrin, in fact, acts much as muscarin 

 does, and iodine salts act like atropia. Cyon bases upon 

 these results the theory that it is the office of the thyroid, 

 although not necessarily the only one, to transform into an 

 organic combination the iodine salts taken into the body, 

 which otherwise would act as poisons to the nerves of the 

 heart and bloodvessels. Not only are the iodine salts thus 

 rendered harmless, but the iodothyrin formed by their union 

 with proteids or proteid-like bodies is beneficial to the 

 action of the vascular mechanism. He attributes the circu- 

 latory symptoms that follow removal of the thyroid (con- 

 striction of the small arteries, marked acceleration and con- 

 sequent weakening of the heart and diminution of the output) 

 to the loss of this regulative influence. It is a remarkable and 

 as yet unexplained fact that in birds thyroidectomy appears to 

 be harmless. The apparent immunity of rodents to this opera- 

 tion is due, it has been suggested, to the presence of sporadic 

 masses of thyroid tissue (accessory thyroid glands), or to the 

 presence of small bodies in the neighbourhood of the thyroid 

 but of a different structure (parathyroids). Some have even 

 gone so far as to assert that, in animals which possess 

 them, it is the parathyroids and not the thyroids which are 

 important, and that the extirpation of the latter is harmless 

 unless the former be also removed. But the matter is not 

 yet beyond the pale of controversy. 



Although no clear proof has yet been given that the secre- 

 tion of the thyroid is influenced by nerves, it is probable 

 that this is the case. Section of the superior and inferior 

 thyroid nerves going to the gland is followed by degenerative 

 changes in it ; and, indeed, extirpation of the gland causes 

 degeneration in the nerves from which the thyroid fibres 

 come, viz., the vagus and its superior and inferior laryngeal 

 branches (Katzenstein). 



Suprarenal Capsules. It had been observed by Addison that 



