THE THYROID AND PARATHYROID BODIES 961 



efficacy of which does not depend so much upon the iodin as upon 

 the character of its combination with other substances. But since 

 organic iodin complexes, such as iodin-protein, are inactive, the chief 

 factor to be determined is liow much active iodin-containing material 

 can actually be liberated from the inactive iodin substance of the 

 gland. 



In order to prove that such an elaboration actually takes place, 

 Rogoff and Marine^ have followed the method of Gudernatch^ and 

 have exposed tadpoles to the influence of iodin-free and hydrolized 

 sheep thyroid, containing varying amounts of available iodin. In 

 the latter case, their growth was retarded, while their differentiation 

 took place at a much faster rate. The rapidity and decisiveness with 

 which these changes are effected, may be employed as a means of 

 determining the intensity of the evolution of the active iodin-con- 

 taining substance. 



A chemical test of even greater delicacy is the nitrile reaction described by 

 Hunt. ^ If so little as 0. 1 mg, of dried thyroid substance per gram of body-weight 

 is fed to a white mouse each day for 10 consecutive days, this animal will survive 

 as much as 10 times the amount of acetonitrile which would prove fatal to any 

 other mouse not having received this treatment. 



It is also of interest to note that the thyroid possesses marked storative quali- 

 ties for iodin. Thus, if iodin is administered to animals with actively hyperplas- 

 tic thyroids, this substance is rapidly stored in this gland and gives rise to definite 

 histological changes, constituting the so-called colloid goiter. Moreover, the 

 greatest storative power is possessed by those glands which are most hyperplastic 

 and contain, to begin with, the smallest amount of iodin. It matters little whether 

 the iodin is administered at this time intravenously in the form of a salt or is per- 

 fused through the excised gland. 



The Function of the Thyroid and Parathjnroids. — It has been 

 noted above that the extirpation of the thyroid of carnivorous animals 

 proves fatal almost without exception, but does not seriously incon- 

 venience the herbivora. Whatever deviations from this general rule 

 may have been observed, they are due in all probability to peculiar- 

 ities in the distribution of the parathyroid bodies. Inasmuch as these 

 structures were not recognized as an anatomical entity until late dur- 

 ing the period of thyroid experimentation, many of these symptoms 

 have undoubtedly been ascribed to the loss of this organ, although 

 actually caused by the loss of the parathyroids. Besides, since the 

 latter also appear in the form of accessory masses along the trachea, 

 they may have escaped detection altogether. It need not surprise us, 

 therefore, to find that the clinical picture following the removal of the 

 thyroid and parathyroids, remained incomplete for some time after 

 the beginning of this kind of experimentation. 



Very shortly after the discovery of the parathyroids, Gley and 

 others proved that the symptoms following the extirpation of the thy- 



1 Jour, of Pharm. and Exp. Therapeutics, ix, 1916, 57 and x, 1917, 99. 



2 Archiv fur Entwick. Mech. der Organe, xxxv, 1913, 457; also see: Graham, 

 Jour. Exp. Med., xxiv, 1916, 345. 



3 Jour, of Biol. Chem., 1, 1905, 33. 



61 



