278 METHODS OF IDENTIFICATION AND STUDY 



6. Filter and divide the filtrate into three parts a, b 

 and c. 



a. Repeat the copper sulphate test, using excess of 

 caustic soda to displace the ammonia from the am- 

 monium sulphate. 



Pink colour = peptone. 



b. Boil with Millon's reagent. 

 Red colour = tyrosine. 



c. Add glyoxylic acid solution and run in concen- 

 trated sulphuric acid. 



Violet ring at upper level of acid = tryptophane. 



Both the tyrosine and tryptophane may be either 

 in the free state or in combination as polypeptid or 

 peptone. 



(B) Diastase. (Converts starch into sugar; e.g., B. 

 subtilis.) 



Medium Required: 



Inosite-free bouillon. 

 Reagents Required: 



Starch. 



Thymol. 



Fehling's soltuion. 



METHOD. 



1. Prepare tube cultivation and incubate. 



2. Prepare a thin starch paste and add 2 per cent, 

 thymol to it. 



3. Mix equal parts of the cultivation to be tested 

 and the starch paste, and place in the incubator at 37 

 C. for six to eight hours. 



4. Filter. 



Test the nitrate for sugar. 



Boil some of the Fehling's solution in a test-tube. 



Add the nitrate drop by drop until, if necessary, a 

 quantity has been added equal in amount to the Feh- 

 ling's solution employed, keeping the mixture at the 

 boiling-point during the process. 



Yellow or orange precipitate = sugar. 



