THE BIOCHEMISTEY OF THE THYEOID GLAND 255 



tailing its chemical properties. The results of these three important 

 papers are summarized below: 



The starting point of the work was the discovery that hydrolysis with 

 sodium hydroxid in alcohol yielded 75 per cent of the iodin in the gland 

 in a dialysable condition, but still in organic combination. The digest 

 contained two types of compounds, one soluble in acid, and another insolu- 

 ble. The group of substances soluble in acids consisted chiefly of amino- 

 acid complexes. The iodin compound in the group was precipitated to a 

 large extent by mercuric sulphate, and almost quantitatively with silver 

 sulphate and magnesium oxid, but was largely decomposed by this treat- 

 ment. The iodin was easily split off by oxidizing agents. The group of 

 substances insoluble in acids was acidic, had the general properties of a 

 fatty acid, was easily soluble in dilute alkalis, and was reprecipitated by 

 any acid. After removal of fatty acids and sulphur with petroleum ether 

 the product contained four per cent of iodin. By repeated solution in 

 alkali and precipitation with acid, and subsequent partial extraction with 

 ethyl acetate the ester-soluble fraction contained 13-14 per cent of iodin. 

 Further hydrolysis of this group of substances with sodium hydroxid at a 

 high temperature split of lauric acid and tryptophan. 



Similar cleavage was obtained by hydrolysing fresh thyroids with 

 aqueous sodium hydroxid for 24 hours. The fats were removed as sodium 

 soaps, and a clear alkalin filtrate of the hydrolysed thyroid proteins con- 

 taining practically the entire iodin content was obtained. Acidifying this 

 gave a fine flocculent precipitate, which, when dried, amounted to 0.1 per 

 cent of the total weight of fresh gland, and contained 26 per cent of the 

 total iodin, so that approximately three-fourths of the total iodin-contain- 

 ing compounds were soluble in acid, and only one-fourth insoluble. This 

 proportion is constant at different times of the year and in different 

 samples from different species, and is considered to represent the equilib- 

 rium existing in the gland between the completed specific iodin compound 

 and the materials used for building it up. 



The precipitate, heated to about 40 to 50 C. in aqueous suspension, 

 changed to a black tarry mass, soluble in acid alcohol, and repeated pre- 

 cipitation with barium hydroxid from this solution gradually concentrated 

 the iodin compound until it contained 47. 3 per cent of iodin. This prepa- 

 ration was dissolved in 95 per cent alcohol, evaporated on a water-bath to 

 dryness, and accidentally heated for an hour. The white residue was in- 

 soluble in alcohol and contained 60 per cent of iodin. About 200 mg. of 

 thyroxin was obtained in this way; but preparation on the large scale 

 proved impossible until various sources of error had been eliminated, 

 which were : a deleterious effect of temperature during precipitation with 

 acid; initial alkaline hydrolysis in all metal tanks except Ni, Au, Ag, and 

 Pt breaks off iodin from organic combination ; carbondioxid plays an im- 

 portant role in the separation of thyroxin from impurities, but the tern- 



