248 SCIENCE PROGRESS 



(1909), and more recently by E. R. Hoskins and by Herring 

 (1916). 



As might be expected, the symptoms of hyperthjToidism 

 are the opposite of those of hypothyroidism, and result from 

 increased functional activity of the tissues generally. 



The same changes occur in man in the disease known as 

 Exophthalmic Goitre, first described by Parry (1825), and 

 later by Graves (1835) and Basedow (1840). Tremors, exoph- 

 thalmos, tachycardia, high blood-pressure, a high metabolic 

 rate, and nervousness are typically present, and, in addition, 

 there is usually a marked swelling of the thyroid gland in the 

 neck. The similarity with the symptoms produced by exces- 

 sivejthyroid feeding is too close to avoid the conclusion that 

 the ' mechanism is the same in both cases. Moreover, the 

 enlargement of the gland and the histological picture of hyper- 

 secretion adds to the probability, even although no definite 

 proof of an increase of thyroid secretion in the circulating 

 blood is available. 



Lastly, it is of interest that both myxoedema and exoph- 

 thalmic goitre occur more commonly in women, in whom the 

 thyroid normally enlarges during menstruation and especially 

 during pregnancy. 



The Function of the Thyroid in the Lower Vertebrates. — 

 Most work has been done on amphibians, and according to 

 Gudernatsch (19 12), who initiated these experiments, feeding 

 tadpoles with thyroid caused them " to metamorphose . . . 

 weeks before the control animals did so." Miniature frogs, 

 with well-formed limbs and abdominal and other organs, could 

 be produced in less than three weeks in this way. Thyroi- 

 dectomy, on the contrary, arrests differentiation [Hoskins and 

 Morris (191 6)], the tadpoles remaining larval although the 

 gonads continue to develop [Allen (191 7)]. The above results 

 are strictly comparable with those obtained in mammals, and 

 have been repeatedly confirmed. Gudernatsch 's discovery is 

 of importance in that it furnishes a reliable method of detect- 

 ing and estimating thyroid. 



The Nature of the Thyroid Secretion. — ^Although the actual 

 secretion of the thyroid has never been obtained, an extract of 

 the gland is believed to contain it. At any rate, Baumann 

 (1875) was able to prepare an organic compound of iodine from 

 the gland, which acts in the same way as the extracts. Iodine 

 is present in nearly all normal thyroids, and it was shown by 

 Reid Hunt (1904) that the activity of the gland varies directly 

 with its iodine content. Lenhart (191 5), employing tadpoles, 

 arrives at the same conclusion. The iodine, however, may 

 be combined either in an active or an inactive form [Kendal 

 (191 6), Marine and Rogoff (1916)], hence the iodine content, as 



