CH. VIII.] INDOL. 227 



digestion carried out as described on p. 88, except that it can proceed for 10 to 

 1 6 days if convenient. At the end of the digestion period the mixture is 

 transferred to a flask, treated with 150 cc. of a i in 10 dilution of pure concen- 

 trated hydrochloric acid, heated in a steamer for 30 to 60 minutes and filtered. 

 The filtrate is treated with 5 per cent, sodium hydroxide until it is faintly 

 alkaline to litmus. The resulting fluid or " stock broth " can be preserved in 

 a stoppered bottle for a very considerable period if a little toluol be added. 

 One part of the stock broth is treated with two volumes of a 0-4 per cent, 

 solution of sodium chloride and the reaction adjusted to P H = 7-3 to 7-4 by the 

 method given in Ex. 322, Note 3. The " tryptic broth " thus obtained is 

 distributed into convenient flasks, which are plugged with cotton wool and 

 sterilised in the autoclave. 



A flask (labelled A) of the cooled sterile broth is inoculated with a culture 

 of B. coli (obtainable from a bacteriological laboratory) under the precautions 

 usually adopted to prevent accidental contamination, incubated for 2 days or 

 longer. For comparison an uninoculated flask (labelled B) of the sterile 

 broth is also incubated. 



269. Ehrlich's test for indol. To about 3 cc. of A and of B 



add an equal volume of Ehrlich's reagent (seep. 390). A fine red 

 colour appears in A, but not in B. 



NOTE. If the test does not succeed it is usual to add 3 cc. of a saturated 

 solution of potassium persulphate. The author has never been able to 

 recognise the advantage of this in improving the delicacy of the test. 



270. Nelson's vanillin test for indol. To about 3 cc. of A 

 and B add about 5 drops of a 5 per cent, solution of vanillin in 

 alcohol and then about 3 cc. of pure concentrated hydrochloric acid. 

 An orange colour is produced in A, due to the presence of indol or 

 scatol. In B a slight purplish tint may develop on standing, due to 

 a reaction with unchanged tryptophane. 



271. Destruction of tryptophane by B. coli. To 5 cc. of A and 



B add a drop or two of acetic acid and then bromine water, drop by 

 drop, until no further increase in the colour is obtained. Warm 

 slightly, add 5 cc. of butyl or amyl alcohol to each, shake and allow 

 to stand. The alcohol layer is more deeply coloured in B than in A, 

 owing to the conversion of the tryptophane to indol and scatol. 



272. Tryptophane is the only mother-substance of the indol 

 bodies. 100 grams, of commercial casein are hydrolysed by boiling 

 with 500 cc. of i in 4 sulphuric acid for 12 to 16 hours under a reflux 

 condenser. The resulting dark purple solution is diluted with water 



