960 THE INTERNAL SECRETIONS 



thyroid and a flooding of the system with an excessive amount of this secretion, 

 is well illustrated by the fact that the partial extirpation of this organ gives rise to 

 an almost immediate amelioration of these symptoms. In fact, in many cases 

 it suffices to reduce the vascularity of this organ by the ligation of one of its arteries. 

 Kocher states that these operative measures resulted in 76 per cent, of his cases in a 

 complete cure and in another 14 per cent, in a decided improvement. The mor- 

 tality which amounts to about 3 per cent., is referable chiefly to erroneous diag- 

 nosis. Simple hyperthyrosis is characterized by a slight swelling of this gland, i.e., 

 by a latent increase in its size and a few of the milder symptoms enumerated above. 

 It occurs most frequently in young women, and is temporary in its nature. 



The Nature of the Active Principle of the Thyroid. Much un- 

 certainty still prevails regarding the nature of the active agent 

 contained in the secretion of this gland, although it seems established 

 that it is derived from the colloid material of its vesicles. In this connec- 

 tion, it is of interest to note that a substance has been isolated from 

 thyroid tissue by Baumann, 1 to which he has given the name of 

 iodothyrin or thyroidin. It contains as much as 9.3 per cent, of its 

 dry weight as iodin. While the action of this substance has not been 

 definitely ascertained, it seems certain that it is at least closely 

 associated with the activity of this gland. This is shown by the fact 

 that it is always present in normal glands and that the minimun amount 

 of iodin necessary to maintain the usual histological picture of thyroid 

 tissue, does not fluctuate materially in any given species. Moreover, in 

 cases of hyperplasia the iodin content is invariably below the minimum 

 value of 0.1 per cent, of the dried gland; in fact, no demonstrable 

 quantities of this substance are ever present in extreme conditions of 

 goiter. Very beneficial results have been obtained with this substance 

 in the treatment of myxedema and goiter. Hunt 2 furnishes the fol- 

 lowing interesting analyses: 



Per cent, of 

 Thyroid of iodin 



Children None 



Maltese kid None 



Guinea-pig . . . . 05 



Dog 0.06 



Cat . 08 



Sheep 0. 17 



Beef 0.25 



Hog 0.33 



Human 0.23 



Human in goiter . 04 



A similar but less complex body has recently been isolated by 

 Kendall 3 which he calls thyro-oxy-indol or thyroxin and to which he 

 gives the formula: CiiHi O 3 NI 3 . It is claimed that this substance 

 exerts as powerful an influence upon cretinism and myxedema as 

 desiccated thyroid. Thus, it may be concluded that the active prin- 

 ciple of this internal secretion is an iodin-containing hormone, the 



1 Zeitschr. fur physiol. Chemie, xxi, 1896, 481. 



2 Studies on Thyroid, Bull. Hygienic Lab., Washington, 1909, No. 47. 



3 Am. Jour, of Physiol., Proc., xlv, 1918. 



