MICHIGAN ACADExMY OF SCIENCE. 16& 



THE USE OF TRYPTOPHAN IN CULTURE MEDIA FOR DETEC- 

 TION OF INDOL PRODUCTION. 



S. F. EDWARDS. 



The object of the investigation was to contribute to onr knowledge 

 of the source of indol as produced by micro-organisms in their action 

 on proteids, and to prepare, if possible, a medium which would give more 

 uniform and more satisfactory results than the media commonly em- 

 ployed for the determination of indol production. 



Froni the results obtained by Hopkins and Cole, (Jour. Pliys., 27^ 

 1901-U2), working Avith the end products of proteid digestion, they 

 conclude that the source of indol is the tryptophan group of the proteid 

 molecule. They showed that the characteristic Adamkiewicz reaction 

 could be obtained only when the acetic acid employed contained glyoxylie 

 acid, and that the reaction is not a furfurol reaction, as was previously 

 supposed, but is due to the presence in the proteid molecule of the 

 tryptophan body. 



In our isolation of the tryptophan, we followed the method of these 

 two workers which briefly is as follows : commercial casein is digested 

 with trypsin in a dilute solution of sodium carbonate until the test 

 shows a maximum reaction for tryptophan, Avhen the mixture is heated, 

 filtered, and treated with sulphuric acid, the precipitate of calcium sul- 

 phate being filtered off'. Mercuric sulphate is now added in excess, the 

 resulting bulky precipitate is filtered oft', washed with dilute sulphuric 

 acid, and decomposed with hydrogen sulphide, after removal of which, 

 the substance is re-precipitated by again adding excess of mercuric sul- 

 phate, and the mercury compound is removed in the form of sulphide as 

 before. The sulphuric acid liberated on decomposition of the mercury 

 compound is removed by precipitation with barium hydroxide, and the 

 tryptophan is crystallized from alcohol. 



The substance separates in the form of fine pearly white plates which 

 are moderately soluble in cold water, and freely soluble in hot water. 

 Aqueous solutions are markedly acid to litmus. It is sparingly soluble 

 in absolute alcohol, cold or hot. In moderately strong aqueous solutions, 

 if sufiicient glyoxylie acid be present, the addition of pure sulphuric acid 

 I>roduces a deep indigo color, a greenish zone being seen next the acid 

 if the latter is allowed to remain subnatant. With weak solutions the 

 color is exactly the same as that produced by the original proteid. A 

 solution of one part to ten thousand gives a well marked color. 



The gyoxylic acid is prepared by adding to a saturated solution of 

 oxalic acid in a tall cylinder about sixty grams per litre of sodium 

 amalgam. When all the hydrogen has been evolved, the solution is 

 filtered, and diluted two or three times, and used in exactly the same 

 way as the glacial acetic acid in the Adamkiewicz test. 



Bromine water, in aqueous solutions of tryptophan, excess being 

 avoided, produces a fine rose-red color, and if the mixture be shaken 

 with amyl alcohol, the colored product is taken up by this reagent. 



