IDENTIFICATION OF THE TYPHOID BACILLUS 413 



2. Cloudiness with, a watered-silk appearance in broth culture. 



S. No liquefaction of gelatin. 



(ii) If conforming to these requirements it remains to determine if 

 the organism (which must of course be investigated in pure -culture) be a 

 typhoid or colon bacillus. 



It is now that difficulties arise, though if what has been said in the fore- 

 going chapters be recalled it seems impossible to confuse typical specimens 

 of the two organisms. The motility, the characters of the flagella, the 

 appearance of the growth on potato, the indol reaction, a study of the fer- 

 mentation properties and the agglutination test should furnish a sure means 

 of diagnosis. 



Unfortunately some strains of the colon bacillus readily lose when grown, 

 for instance, symbiotically with the typhoid bacillus (Remy) or a Pasteurella 

 (Lesage), etc. their capacity to produce indol and some of their fermenta- 

 tion properties ; other strains are very motile, while others again yield a 

 very scanty growth on potato and on gelatin grow like the typhoid bacillus. 

 Similarly, some strains of the typhoid bacillus are only slightly motile, and 

 their flagella can only be stained with difficulty : others give a slightly 

 pigmented growth on potato resembling cultures of the colon bacillus : 

 finally, when grown in the presence of the colon bacillus or after passing 

 through human tissues some strains lose their characteristic property of 

 being agglutinated by antityphoid serum. Hence a certain amount of con- 

 fusion arises which is further increased by the existence of a whole group 

 of bacilli very closely related to the typhoid bacillus and having properties 

 intermediate between it and the colon bacilli (paratyphoid bacilli, Chap. XXV.). 



It will therefore be clear that for accurate diagnosis it is necessary to study 

 several of the characteristics of the organism. The table below gives a list 

 of the tests on which the diagnosis should be based. The investigation of 

 the fermentation reactions, the production of indol, the characters of the 

 flagella and the agglutinating properties will in the majority of cases afford 

 sufficient information upon which to determine whether the organism is a 

 typhoid or a colon bacillus. When an organism has all the characteristics 

 of the typhoid bacillus except that it is not agglutinated by an antityphoid 

 serum it must be tested as indicated under 14 in the table. If the serum of 

 a guinea-pig which has been inoculated every other day for a fortnight with 

 2 c.c. of a forty-eight-hour old broth culture of the organism under investiga- 

 tion agglutinate an authentic typhoid bacillus in a dilution of at least 1 in 

 40 (Remy) the organism must be regarded as a strain of the typhoid bacillus. 

 Finally the two last tests (15 and 16) in the table will be found very valuable 

 and should permit of the identification of the organism in even the most 

 difficult cases. 



METHOD OP DIAGNOSIS. 



COLON BACILLUS. 



TYPHOID BACILLUS. 



1. Culture in carbonated 

 lactose-broth. 



2. Stroke culture on lit- 

 mus-lactose-gelatin. 



3. Single colonies on lit- 

 mus-lactose-agar. 



Abundant gas -formation 

 (12-36 hrs.). 



The colour of the litmus 

 is first changed to red 

 then to a pale brown 

 along the stroke. 



Red colonies. 



No gas formation. 



The colour of the litmus 

 is unchanged. 



Blue or violet colonies. 



