262 A. T. CAMERON 



dividuals the nitrogen excretion was increased, and physiological symp- 

 toms appeared similar to those produced by overdoses of thyroid. 

 This same observer made a detailed investigation into the comparative 

 effects of orally administered thyroxin and thyroid in thyroid diseases and 

 found that the therapeutic effect of thyroxin is unchanged by passage 

 through the gastro-intestinal tract. The test of decrease in growth-rate 

 and hypertrophy of body organs (rats) has now been applied to thyroxin, 

 which gives results similar to those obtained with thyroid itself; this 

 affords an additional rigorous proof of the identity of thyroxin with the 

 essential chemical compound secreted by the gland. (Cameron and Car- 

 michael, 1921.) 



While iodothyroglobulin produces physiological and. metabolic actions 

 resembling those produced by thyroid, in some respects these do not appear 

 to be much greater than those produced by other organic iodin compounds 

 or complexes such as gorgonin, spongin, etc. These effects are, it must be 

 remembered, produced after passage through the alimentary tract where 

 hydrolysis takes place and some smaller iodin compound is actually 

 absorbed. On the other hand thyroxin appears to produce all the specific 

 effects of thyroid, in a degree bearing some relation to the relative iodin 

 content, and this whether injected directly into the blood stream or given 

 through the alimentary tract. On a priori grounds the active part of the 

 thyroid secretion should consist of a relative simple compound of this 

 nature. The whole mass of evidence leads to the conclusion that thy- 

 roxin is one of the active compounds secreted by thyroid. Before it 

 can be definitely stated that it is the only specific compound, it is necessary 

 to know more of the hydrolysed products containing 75 per cent of the 

 iodin in the gland, soluble in acids, of amino-acid nature, and which, 

 according to Kendall (1915) possess some physiological activity. 



The Relationship Between Iodin Content and Thyroid Activity. It 

 was shown by Roos (e) (1899) that thyroid glands rich in iodin content 

 produce greater increase in nitrogen excretion and greater loss of body 

 weight than those poor in iodin, while "iodin-free" glands (i. e., containing 

 too small an amount to be detected by Baumann's method of analysis) pro- 

 duced no effect. Fonio (1911) also found that the increase in nitrogen 

 excretion is proportional to the iodin content of the thyroid fed, and 

 Pcillon (1910) obtained the same result. Heavy doses of iodin-rich 

 thyroid are more toxic than corresponding doses of a thyroid containing 

 less iodin (Stoland, 1912). The metabolic and physiological activity of 

 iodothyroglobulin is proportional to the iodin content (Oswald, 1902, 

 191G, Lanz). 



The connection between iodin content and thyroid activity has been so 

 widely accepted that certain pharmacopeias require a definite iodin percen- 

 tage. Van Os reports adversely on this method of standardization. 



Cameron and Carmichael (1920) found that the decrease in rate of 



