430 BACTEUIOLOOY. 



Medium No. 2 consists of: 



Witte's peptone . . .2.0 per cent, in distilled water. 



Mannite ... .0.1 



Both media are to be sterilized, the reaction brought 

 to the litmus neutral point with caustic potash solu- 

 tion, and enough litmus tincture then added to them to 

 cause a distinct, though not too intense, purple color. 

 After this they are to be again sterilized, when they 

 are ready for use. 



After 20 hours at 37^-38° C. typical colon bacilli 

 and the varieties of this organism develop in both solu- 

 tions, but produce acid only in medium No. 1. 



The typhoid bacillus grows only in medium No. 2, 

 and its growth is accompanied by the production of 

 an acid reaction. 



The growth of bacillus coli in medium No. 2 is ac- 

 companied by a slight aUialine reaction. 



The alterations in reaction are indicated by the cor- 

 responding changes in the color of the litmus tincture 

 in the media. 



It is interesting to note that in this test the usual 

 reactions produced by these organisms in peptone media 

 containing the ordinary fermentable carbohydrates, such 

 as glucose and lactose, are reversed. 



The authors state that this method has thus far shown 

 itself to be infallible for the differentiation of cultures 

 of typhoid and colon bacilli obtained by them from 

 every available source. 



Hunter^ recommends the use of neutral red as a dif- 

 ferential test. He employs it iu the proportion of 0,5 

 to 1 .0 c.c. of a saturated watery solution to 10 o.c. of 

 nutrient agar-agar. The reducing action of the colon 



1 Hunter: Tlie Lancet, March 2, 1901. 



