REACTIONS OF B. TYPHOSUS AND B. COLT. 309 



nitrite and sulphuric acid, yellow nitric acid (which of 

 course contains nitrous acid) may be employed alone. 

 The typhoid bacillus never gives this reaction, and all are 

 agreed that this is one of the most valuable differential 

 tests between the two bacilli. The only fallacy to which it 

 appears liable, is that while the B. typhosus never gives it, 

 it appears that some varieties of the B. coli fail to produce it 

 also. Attention must be directed to one important point. 

 We have found that, as in the case of this same indol test 

 for cholera, great care must be taken in the selection of 

 the peptone in preparing the bouillon to be used. Not 

 every specimen of commercial peptone will give the 

 reaction. A series of peptones must, therefore, be tested, 

 and when a sample is obtained which gives the reaction 

 well, it must be preserved for subsequent use for the same 

 purpose. We may here say in conclusion that indol is not 

 produced by the B. coli in the presence of lactose. The indol 

 reaction must thus not be sought for in a lactose medium. 



(4) Growth on Phenolated Gelatine. It was at one time thought 

 that gelatine with .2 per cent carbolic acid added inhibited the growth 

 of all bacteria but the typhoid bacillus. It has been found, however, 

 that the growth of the B. coli is also unaffected by such a medium, 

 though it prevents the growth of most putrefactive organisms which 

 liquefy gelatine. 



(5) Widats Serum Method for Distinguishing B. 

 from B. coli. This will be described later (p. 322), and 

 here we need only say that it is probably the most important 

 means of distinguishing between the two bacilli. 



It will thus be seen that the diagnosis between the B. 

 typhosus and the B. coli is a matter of no small difficulty. 

 The points to be attended to in making such a diagnosis 

 are given in the accompanying table. There is no evidence 

 that the one organism ever passes into the other. Klein 

 has found that both after prolonged sojourn in distilled 

 and tap water, and also after passage through the bodies of 

 a series of animals, each organism still preserves its original 

 characters. Statements as to their identity usually rest on 

 theoretical considerations, or on purely negative evidence. 



