310 THE DUCTLESS GLANDS 



tained in the colloid substance, though there is some evidence 

 that the cells of the vesicles also contain a certain amount. 



In algae most of the iodine is in soluble organic (non-protein) 

 combination, a trace only being present as iodide. Drechsel 

 found an iodo-amino-acid in the skeleton of a coral, which was 

 later identified as di-iodo-ty rosin. Dibrom-ty rosin is also 

 found in corals and sponges. It is said that p.-iodophenyl- 

 alanine is present in sponges. 



None of these can be isolated from the thyroid. In the 

 gland most if not all the iodine is in organic combination. 

 Some observers state that there is a small amount of iodide 

 present. Baumann boiled thyroid glands with sulphuric acid. 

 The residue was extracted with alcohol and evaporated to 

 dryness. The product was called thyroiodin or iodothyrin. 

 It contained 10 per cent, of iodine, and amounted to about 

 4 per cent, of the total weight of the dried thyroid. It has 

 been found that Baumann's product was not of a constant 

 chemical constitution, and it has been suggested that the 

 iodine compound present was iodotryptophane. Various 

 other thyroid preparations have been made and have been put 

 forward as the " active principle " of the thyroid gland, 

 lodothyroglobulin (Oswald) is possibly a definite compound 

 and exists as such in the thyroid gland. 



In 1919 Kendall announced the isolation of a definite 

 crystalline iodine compound which he calls " thyroxin." His 

 method of isolation is given as follows : " The fresh thyroid 

 glands are hydrolyzed in 5 per cent, sodium hydroxide in a 

 nickel kettle, the fats are removed by rendering the sodium 

 soap insoluble, and the clear alkaline filtrate is cooled and 

 acidified. The acid insoluble constituents containing practi- 

 cally 100 per cent, of the thyroxin present are filtered off. This 

 material is redissolved in sodium hydroxide and reprecipitatrd. 

 using hydrochloric acid. The precipitate is now air-dried and 

 is dissolved in 95 per cent, alcohol. The excess hydrochloric 

 acid which remains in the air-dried precipitate is neutralized 

 with sodium hydroxide until it is almost neutral to moistened 

 blue litmus paper. A heavy, black, tarry precipitate forms, 

 which may be removed by filtration. The alcoholic filtrate 

 is treated with barium hydroxide by adding a hot, very con- 

 centrated aqueous solution of the hydroxide to the alcohol, 

 and refluxing. The treatment with barium removes some 



