260 A. T. CAMERON 



priva, which, outside of man, is particularly liable to misinterpretation, and 

 on the influence on metabolism, which alone lends itself to any accuracy. 



The acetonitril test of Keid Hunt is no longer considered specific for 

 thyroid (Beebe, Olds, Lussky, Allen), while the hastened metamorphosis 

 of thyroid-fed tadpoles, discovered by Gudernatsch (&) (c), and confirmed 

 by many other workers, has been shown by Swingle to be produced also by 

 inorganic iodin, by iodids, and by iodoform, and to be specific for iodin 

 and not for thyroid. This throws doubt on experiments such as those of 

 Marine and Rogoff (&), in which an attempt was made to ascertain the 

 rapidity with which the intact gland elaborates its specific iodin compound, 

 and in which the iodin test was used also (1916, also Rogoff and Marine). 



The metabolic method available is the measurement of the increased 

 excretion of the products of catabolism, especially phosphates and total 

 nitrogen, which invariably follows upon the oral administration of fresh 

 or desiccated thyroid, and which is usually accompanied by loss of body 

 weight. There is some evidence that iodin increases phosphorus excretion, 

 but that of nitrogen excretion is unaffected. A second method is prob- 

 ably available; thyroid feeding definitely diminishes the rate of growth 

 in young white rats (Cameron and Carmichael), and at the same time 

 causes hypertrophy of the organs concerned with increased metabolism, 

 namely, heart, liver, pancreas, kidneys, adrenals, etc. (Hoskins, 1916, 

 Herring), and this effect is specific as contrasted with iodids (Cameron 

 and Carmichael). 



It should be remembered in considering the following statements that 

 thyroid gland, administered by way of the alimentary tract, will, like 

 other similar tissue, be broken down to small unit compounds before 

 absorption, and no such compounds as iodothyroglobulin will be absorbed 

 into the blood-stream as such. lodothyrin is that part of thyroid and of 

 iodothyroglobulin that resists solution under pepsin digestion, while tryp- 

 sin splits off three-fourths of the iodin from organic combination (Oswald, 

 1899). Diiodotyrosin, fed to animals, appears incapable of assimilation 

 as such, and most of the iodin is split off and excreted as iodid (Abder- 

 halden and Slavu, Oswald (g), 1910). No information is yet available as 

 to the effect of digestive enzymes on thyroxin, but its physiological action is 

 stated to be the same whether it be administered orally or intravenously. 



Discussion of Individual Substances. lodothyrin. This preparation 

 has played such a considerable part in thyroid literature that it seems de- 

 sirable to consider in some detail the evidence for and against its being 

 the internal secretion of the thyroid. Baumann and Boos stated that it 

 has all the characteristic properties of thyroid, with a more rapid physio- 

 logical action than the fresh gland or tablets. Baumann and Goldmann 

 stated that it prevents the appearance of cachexia thyreopriva in thyro- 

 dectomized dogs. This view is supported by Hildebrandt and Irsai and 

 denied by Notkin (6), 1896, and Wonnser. Roos (1896), experimenting 



