288 BACTERIOLOGICAL EXAMINATION OF WATER. 



litre are added. The broth is then boiled in the steam steriliser 

 for twenty minutes, filtered, poured into the test-tubes, and 

 sterilised for twenty minutes on the day it is made and the two 

 succeeding days.'" 



Nitrate-broth. This medium is prepared by adding 0*1 per 

 cent, of potassium nitrate to nutrient broth, diluted with sterile 

 water, so that the medium contains only 5 per cent, broth, viz., 

 KNO 3 O'l gramme, broth 5 c.c., sterile water 95 c.c. If pure 

 broth is used the medium turns almost black on adding Nessler 

 solution, so that it is impossible accurately to determine the 

 presence of ammonia. 



