THE COLON GROUP OF BACILLI 129 



the dextrose broth. Hale and Melia (1910) find that 

 this gives results in as high a dilution as by the use of 

 dextrose broth and with the clear-cut results of lactose 

 bile. 



The Aesculin Test. A test for the colon group which 

 has attracted much interest during the last few years 

 is the fermentation of the glucoside aesculin. B. 

 coli effects a hydrolytic splitting of this substance, 

 producing sugar and a substance called aesculetin, 

 which reacts with iron citrate to produce a dark brown 

 salt. Harrison and van der Leek (1909) have used 

 broth or agar made up with i or 2 per cent Witte's 

 peptone, .5 per cent sodium taurocholate, .1 per cent 

 aesculin and .05 per cent citrate, and find that the 

 black colonies with a black halo produced by the colon 

 group of organisms are highly characteristic. Of 

 60 samples of water which showed blackening of 

 aesculin broth, all proved to contain B. coli. Hale 

 and Melia (191 1) have shown that two species of 

 streptococci, the aurococcus, and the bacillus of 

 pneumonia, also give the aesculin reaction and that 

 in the absence of the bile salt which the aesculin 

 medium contains a number of other forms may ferment 

 this glucoside. 



On the whole we do not think it has been shown 

 that aesculin has sufficient dift'erential value to war- 

 rant its inclusion in enrichment media to be used in 

 the colon test. It appears that the anaerobic B. welchii 

 is practically the only form outside the colon group 

 which produces a characteristic reaction in lactose 

 bile and not in aesculin-bile salt media. It may prove 



