IX 



Here also the influence of varying acidity and alka- 

 linity is clearly exhibited in the obtained results. 



From Tables XII, XIII and XIV, where the quantity 

 of lactose added is respectively 1, 2 and 3% it will be 

 seen, that with an increasing quantity of lactose the capa- 

 city of B. typhosus to alter the red colour to yellow increa- 

 ses, while the power of B. coli decreases. This is an im- 

 portant fact. From it arises the possibility of using neu- 

 tral red as a means for distinguishing B. typhosus from 

 B. coli. The reaction modified in this way, (i. e. 3 % 

 lactose neutral red bouillon) though it cannot be regar- 

 ded as an infallible test, gives more equable and reliable 

 results than that recommended by the earlier investi- 

 gators, at all events, this has been the case with those 

 bacilli, which we have had at our disposal. 



