122 BA CTERIOL OGY. 



Peckham has also demonstrated that where bacteria 

 have the property of forming indol and also of fer- 

 menting carbohydrates, their proteolytic function, as 

 evidenced by the appearance of indol as a product 

 of metabolism, may be completely suppressed by the 

 addition of such fermentable carbohydrates as glucose, 

 saccharose, and lactose to the proteid solution in which 

 they are developing.^ 



Gorini suggests the advisability of testing the purity 

 of all peptone preparations before using them, by means 

 of the reaction that they exhibit with Fehling's alka- 

 line copper solution. Under the influence of this, 

 agent pure peptone in solution gives a violet color (the 

 biuret reaction), which remains permanent even after 

 boiling for five minutes. If, instead of a violet color, 

 there appears a red or reddish-yellow precipitate, the 

 peptone should be discarded, as in his experience no 

 indol is produced from peptone giving this reaction. 

 Both the peptone solution and that of the copper (par- 

 ticularly the latter) should be relatively dilute in order 

 for the reaction to be successful. 



Peptone rosoUe acid solution. Peptone solution con- 

 taining rosolic acid serves well for the detection of alter- 

 ations in reaction. It consists of the peptone solution 

 of Dunliam, to each 100 c.c. of which 2 c.c. of the 

 following solution are added : 



Eosolic acid (coralline) . . 0.5 gramme. 



Alcohol (80 per cent.) .... . lOO c.c. 



This is to be boiled, filtered, and decanted into clean, 

 sterilized test-tubes, about 8 to 10 c.c. to each tube. 



1 See Journal of Experimental Medicine, 1897, vol. ii. p. 549. 



