256 A. T. CAMERON 



perature must be kept below 50-60 C. ; the thyroxin content of different 

 samples of desiccated thyroid varies as much as 400 per cent. 



The present method in use is, according to Kendall (i) (1919), as fol- 

 lows: "The fresh thyroid glands are hydrolysed in 5 per cent sodium 

 hydroxid in a nickel kettle, the fats are removed by rendering the sodium 

 salts insoluble, and the clear alkaline filtrate is cooled and acidified. The 

 acid insoluble constituents containing practically 100 per cent of the thy- 

 roxin present are filtered off. This material is redissolved in sodium 

 hydroxid and reprecipitated, using hydrochloric acid. The precipitate is 

 now air-dried and is dissolved in 95 per cent alcohol. The excess hydro- 

 chloric acid which remains in the air-dried precipitate is neutralized with 

 sodium hydroxid until it is almost neutral to moistened blue litmus paper. 

 A heavy, black, tarry precipitate forms, which may be removed by filtra- 

 tion. The alcoholic filtrate is treated with barium hydroxid by adding a 

 hot, very concentrated aqueous solution of the hydroxid to the alcohol, and 

 refluxing. The treatment with barium removes certain heavy dark impuri- 

 ties. A small amount of sodium hydroxid is added to the nitrate and 

 carbon dioxid is passed through the solution. The barium and sodium 

 carbonate are removed by filtration, and the alcohol is distilled. The last 

 traces of alcohol are removed by heating in an evaporating dish. The 

 aqueous residue is now acidified with hydrochloric acid. The precipitate 

 is dissolved in alkalin alcohol, carbon dioxid is passed through the solution, 

 the precipitated sodium carbonate is removed, and the alcohol evaporated. 

 The last traces of alcohol are removed by heating on a water bath and 

 the solution is allowed to stand. The monosodium salt of thyroxin will 

 separate at this point. The yield is not quantitative, and it must be further 

 purified by dissolving in alkalin alcohol, passing in carbon dioxid, distill- 

 ing the alcohol, and allowing the monosodium salt to crystallize a second 

 time. This may then be precipitated from an alkaline alcoholic solution by 

 the addition of acetic acid. Resolution in alkaline alcohol and precipita- 

 tion with acetic acid for five or six times removes the impurities and will 

 yield thyroxin containing the theoretical percentage of iodin." 



Writing in 1919, Kendall stated that 33 grams of the compound had 

 been separated from 6550 pounds of fresh thyroid material, made up 

 almost entirely of hog thyroid. 



Thyroxin is stated to be 4-5-6-trihydro-4-5-6-triiodo-2oxybeta-indole 

 propionic acid. It exists in three forms: (i) the keto form with the car- 

 bony 1 group adjacent to the imino, (n) a tautomeric enol form, and (in) 

 a form with an open ring structure (cf. creatin and creatmin). It can be 

 regarded as a derivative of tryptophan. Kendall considers that the third 

 form is that in which thyroxin occurs in the body. 



The change to the open ring form is brought about very easily in the 

 presence of certain substances which are amongst the products of the 

 hydrolysed protein, and which contain the indol nucleus. 



