g2 DETERMINATION OF SPECIES. 
acidity and alkalinity of media, all that is necessary 
is to add to tubes containing equal quantities of 
any of the usual media a calculated amount of a 
standardized solution of hydrochloric acid or of 
sodium hydroxid to obtain the desired reaction. A 
record should be made of cultures upon at least one 
medium reacting +3 per cent., +1.5 per cent., 
neutral, and —1.5 per cent. to phenolphthalein. 
(h) Action upon Carbohydrates.—For the 
methods of determining the action upon carbo- 
hydrates and for measuring the gas production, see 
under Cultures in the Fermentation-tube, page 76. 
(i) Action upon Nitrates.—To determine the 
power of certain bacteria to reduce nitrates to 
nitrites and ammonia, incubate them for seven 
days at 20° C. in the following: 
NITRATE BROTH. 
Peptone, I gm.; 
Potassium nitrate, 0.2 gM. ; 
Tap water,’ I000 ¢.¢c. 
Submit the inoculated tubes and also several un- 
inoculated control-tubes to the following tests for 
nitrites : 
Prepare two solutions : 
I, Naphthylamin, O.I gm. ; 
Distilled water, 20 c.c. 
Boil until the naphthylamin is dissolved ; cool, 
1 Better than distilled water because of the other salts 
present, which favor the growth of the bacteria. 
