134 BACTERIOLOGY. 



ilized in the steam sterilizer in the ordinary way. 

 The most common use to which this solution is put 

 is in determining if the organism under considera- 

 tion possesses the property of producing indol as one 

 of its metabolic products. It is essential for accu- 

 racy that the preparation of dried peptone employed 

 should be as nearly chemically pure as is possible, 

 and indeed the other ingredients should be corre- 

 spondingly free from impurities. Gorini l calls attention 

 to the fact that impurities in the peptone, particularly 

 the presence of carbohydrates, so interfere with the 

 production of indol by certain bacteria that otherwise 

 produce it, that it is ofttimes impossible, under such cir- 

 cumstances, to obtain the characteristic color-reaction of 

 this body, and where it is obtained it is always after a 

 much longer time than is the case where peptone free 

 from these substances has been used. 



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 re- 

 agent pure peptone in solution gives a violet color (the 



1 Gorini : Centralblatt fur Bakteriologie und Parasitenkunde, 1893, 

 vol. xiii. p. 790. 

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



