OKGANOTHEKAPY AND HOKMONOTHEKAPY 85 



I H 



C O 



TT /\ H H / 



*iC C = C-C-C-C 



| H H \ 

 H l OH 



^c c c=o 



1 \// \ | 



* I 



C HHO 

 H H 



It would appear that this substance exerts many if not all of the ther- 

 apeutic actions of thyroid extracts, both laboratory investigations and 

 clinical trials conducted in the Mayo clijiic having demonstrated that it 

 can entirely replace thyroid extract in the treatment of myxedema (Ken- 

 dall (/) (g), 1917, 1918). 1 Thyroxin is very insoluble in alcohol, ether, 

 water, acids, and sodium carbonate, but readily soluble in dilute alkali and 

 ammonia. 



Several authors have claimed the successful isolation in more or less 

 pure form of the active principle or principles of the thyroid, among 

 others, Oswald, who believed that the therapeutic activity was exerted 

 mainly or entirely by a globulin named by him thyroglobin. Beebe's 

 views as to the significance of different substances isolated by him have 

 not been generally accepted. 



Although Kendall's discovery of thyroxin is of great interest and 

 doubtless also will prove of clinical value in the future, for the present 

 more practical importance attaches to the fact that the physiological' 

 activity (and therefore the therapeutic efficiency) of thyroid preparations 

 appears to run parallel to their iodin content, and that this varies within 

 very wide limits, Hunt and Seidell finding, in preparations on the Amer- 

 ican market, a variation of 400 per cent (0.095 to 0.38 per cent). What- 

 ever the true nature of the active principle or principles may be they are 

 relatively stable substances, and resistant to heat so that they may be 

 readily sterilized. 



Absorption and Fate. The active substance or substances are readily 

 absorbed from the alimentary canal and when thus administered produce 

 their characteristic effects. Kendall (i) (1919) found that of 200 mg. 

 of thyroxin injected intravenously, 43 per cent was excreted in 

 the bile and 13 per cent in the urine during the next fifty hours. The 

 rest, he believes, was removed from the blood stream by the thyroid gland. 



1 Kendall (/) (1917) considers it by no means impossible that the thyroid con- 

 tains at least one other active principle, as in the Mayo clinic it has been found that 

 some of the symptoms of myxedema were relieved by certain thyroxin-free fractions of 

 thyroid extract, which were obtained while isolating thyroxin. 



