IMPORTANT PATHOGENIC BACTERIA 1 13 



1. Routine study. — Observe carefully the growth on 

 potato of B. aerogenes. This organism produces an 

 amyloly tic enzym, which manifests itself by gas produc- 

 tion. Gas bubbles frequently appear in the growth 

 on potato. 



2. Special study. — ^In order to test the action of 

 micro-organisms on various carbohydrates, it is neces- 

 sary to eUminate the small amount of sugar in ordinary 

 broth introduced into it by meat extract, which 

 generally contains muscle sugar (glycogen). This is 

 accompUshed by adding to freshly prepared broth a 

 culture of B. coli, which decomposes ' many carbo- 

 hydrates, including muscle sugar. By this method 

 a sugar-free broth is prepared, which may be used as a 

 solvent for any sugar desired. 



Preparation of sugar-free broth for the fermenta- 

 tion tube: 



1. Dissolve by heat: 



Extract of beef x . S grams 



Pepton S grams 



in 500 c.c. water. Broth made from chopped beef 

 (500 g. to I hter) may also be used for this purpose. 

 One per cent pepton should be dissolved in meat in- 

 fusion (see p. 31). 



2. After cooHng, inoculate with a broth culture of 

 B. coli prepared 24 hours previously. 



3. Set aside in the thermostat, for 18-24 hours. 



4. Boil 5 minutes (to kill B. coli), and filter repeat- 

 edly through the same paper until clear. 



5. Adjust the reaction to i per cent acid. 



6. Divide into three equal parts and dissolve i per 

 cent dextrose, lactose, and saccharose, respectively, in 

 each part, and filter again, if necessary. 



