Paratyphoid, A and B. 

 Acid and as 



Q8 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



Instead of this step a mannite fermentation tube, prepared in the 

 manner described subsequently, may be used with advantage, especially 

 when dealing with cases of dysentery (in which case the first step, the 

 incubation with brilliant green, should be omitted). This enables a 

 considerable amount of differentiation to be effected at a single step, 

 thus : 



( Dysentery bacillus, Shiga. 

 No chan e ...... \ Morgan's bacillus, No. i. 



T Typhoid bacillus. 

 Acid, no gas ... ... - Dysentery bacillus, Flexner, Y. 



and Strong. 

 f 

 ...... j Gaertner (B. Enteritidis). 



The next step is a rough test of the agglutinability of the pure culture 

 thus obtained by means of known agglutinating sera. These may be 

 obtained from the Lister Institute, and should be diluted i in 10 or i in 

 20 for use in this way. Place three drops of the sera (typhoid and both 

 paratyphoids) on a slide, take a large loopful of the culture and mix it 

 well with the first drop of serum. Repeat the process with the other 

 drops, burning off the material from your needle after each. Examine 

 the result at once \vith the naked eye, tilting the slide forwards and 

 backwards. Agglutination, if present, is practically instantaneous. 



When other organisms (the dysentery group) are being investigated, 

 suitable sera should be used at this stage. It must, however, be under- 

 stood that sera used in this way only give a rough idea of what we have 

 to deal with, as the agglutinability of bacteria just isolated from the 

 body is not normal. The final stage in the process should consist in 

 cultivating the organism for two or three generations in broth, and 

 making a quantitative examination of its agglutinability by the 

 standard serum : it should be clumped at about the same titre as a 

 known and typical culture of the bacillus in question. 



Next, the chemical action of the bacillus thus isolated is tested on 

 various materials, especially the sugars. The following are the routine 

 media for this purpose : 



Lactose (2 per cent.). Neutral red agar. 



Glucose (2 per cent.). Litmus milk. 



Mannite (2 per cent.). Litmus whey agar. 



Dulcite (i per cent.). Peptone-water (for indol). 



The sugar media are made in peptone-salt-water, coloured with an 

 indicator, and provided with a small tube \vhich is inverted inside 

 the test-tube and filled with the medium (Fig. 23). The indicator shows 

 any production of acid, and if gas is formed it fills the inner tube. 



The indicator may be litmus, but a more delicate one, and one, more- 

 over, which is believed to interfere less with the formation of gas, is 

 acid-fuchsin, decolorized by the addition of caustic soda. To prepare 

 it 4 take a 0-5 per cent, watery solution of acid-fuchsin and add normal 



