THE PARATHYROIDS 487 



these facts Oswald believes that the thyreoglobulin, as first 

 secreted by the glandular epithelium, is free from iodin, and that it 

 combines later with iodin from the circulating blood. As yet it 

 has not been ascertained how the iodin is bound to the proteid. 

 It is well known that large amounts of iodin can be introduced 

 into the proteid molecule, apparently through its substitution for 

 hydrogen in the aromatic radicals (tyrosin, phenylalanin, etc.). 

 Thyreoglobulin is not, however, simply an iodized proteid, for 

 the iodized proteid s that can be artificially prepared do not pos- 

 sess the physiological activity of the thyreoglobulin ; further- 

 more, the saturated iodized proteids contain generally from 5 to 

 12 per cent, of iodin, as contrasted with the 0.3 to 0.8 per 

 cent, of thyreoglobulin. Oswald has shown that in thyreoglob- 

 ulin the iodin is not bound to tyrosin, since this can be 

 removed by tryptic digestion without decreasing the amount of 

 iodin in the rest of the molecule ; possibly the iodin is bound to 

 phenylalanin. 



By decomposing thyreoglobulin by boiling with 10 per cent, 

 sulphuric acid, a body is obtained containing as high as 14.5 per 

 cent, of iodin ; this is the thyroiodin of Baumann, which gives 

 no biuret reaction, yet is physiologically active. The stability 

 of this active constituent of the thyreoglobulin explains the 

 successful administration of thyroid preparations by mouth. It 

 appears to be absorbed unchanged and, unless enormous doses 

 are given, none appears in the urine (Oswald). 



The amount of iodin in the thyroid is greatest in middle age, 

 greater in females than in males, and it is decreased in acute 

 infectious diseases and in tuberculosis, alcoholism, and circula- 

 tory disturbances (Aeschbacher *). 



THE PARATHYROIDS 



Whether the thyroid has any other function than the forma- 

 tion of thyroiodin is as yet unknown. Many claim that the 

 thyreoglobulin does not produce the same physiologic and thera- 

 peutic effects as does the entire gland substance, but even that 

 is not definitely decided. Furthermore, it is difficult to distin- 

 guish between the effects produced by the parathyroid glands 

 and those due to the thyroid itself. The parathyroids were 

 originally considered as but a form of undeveloped accessory 



does not increase the amount of iodin in the thyroid. Coronedi and Mar- 

 chetti (Bivista di Patologia, 1902) consider that administration of fatty com- 

 binations of iodin and bromin may partially compensate for loss of the thy- 

 roid. 



1 Mitt. a. d. Grenzgeb. med. u. Chir., 1905 (15), 269. 



