LABORATORY WORK IN, DAIRY BACTERIOLOGY 



269 



normal. It will, of course, require only i/io as many cubic 

 centimeters, as calculation has shown above would be required 

 of i/io normal. This will bring the culture media to the neutral 

 point. 



e. This medium is now not acid enough for the best bacteria 

 growth. The best reaction is one in which there is 15 cubic 

 centimeters of normal HC1 to each 

 liter of the media (1.5^). Con- 

 sequently to this bouillon there 

 should be added 14.9 c.c. of normal 

 HC1 which will give the desired 

 acidity, 1.5%. 



An example will show this more 

 clearly. Suppose that it required 

 1.5 cubic centimeters of the i/io 

 normal NaOH to neutralize 5 c.c. 

 of the bouillon. Dividing this by 

 five would give .3 c.c. required to 

 neutralize I c.c. Multiplying by 

 995 would give 298 c.c. required 

 for neutralizing a liter. Dividing 

 by ten to reduce this to normal 

 XaOH will give 29.8 c.c. Therefore, 29.8 c.c. normal NaOH 

 is added to the bouillon, giving the neutralizing point. After 

 this, 14.9 c.c. of normal HC1 added to the material will give 

 an acidity, 1.5%. 



/. After obtaining the desired acidity, bring the bouillon to 

 a brisk boil for 15 minutes, after which enough water must be 

 added to restore to the original weight. Heat once more to 

 boiling and filter through filter paper into a sterile flask. Place 

 about 10 c.c. in a few test tubes. Replace the cotton plug in 

 both the flask and test tubes; place the test tubes and the flask 

 in a steam sterilizer and steam for 20 minutes (Fig. 71). Put 

 aside at a temperature of the room for 24 hours, then steam 



FIG. 71 STEAM STERILIZER 



