REACTIONS OF B. TYPHOSUS AND B. COLL 329 



acquire the property of producing indol. The formation 

 of indol by an organism after the first transference to peptone 

 solution from one of the ordinary media may, however, be 

 accepted as evidence in favour of the organism not being 

 the typhoid bacillus. It is to be noted here that the presence 

 of lactose in a medium prevents the production of indol by 

 the B. coli. The indol reaction thus ought to be sought 

 for in a sugar-free 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) The Application of the Agglutination Test in Dis- 

 tinguishing B. typhosus from B. coli. The scope of the 

 application of this test will be discussed later (see Im- 

 munity). Here we may say that a negative result obtained 

 with a suspected B. typhosus culture is of greater value than 

 a positive result obtained with a suspected B. coli culture. 

 It is only to be taken in conjunction with the other means 

 of differentiating the two organisms, and is not strictly a 

 crucial test. 



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. 

 Great difficulties sometimes arise in consequence of a 

 bacillus being found which, while giving a number of the 

 characteristics of either one or the other, fails to give some 

 of the characteristic tests, or only gives them very slowly. 

 This is especially true of organisms related to the B. coli. 



