146 BACTERIOLOGICAL CHEMISTRY LESSON n 



and having placed it in a flask, extract it with distilled 

 water by means of shaking. 



(5) Filter, and pour the nitrate, drop by drop, into an 

 excess of absolute alcohol : a precipitate appears. 



(6) Allow the precipitate to settle. Separate off the 

 alcohol, and dry the residue at 45 C., to drive off the 

 alcohol. 



(d) Bacterial extract. 



(1) Inoculate twenty agar-agar tubes with the Bacillus 

 pyocyaneus (streak cultures), and when copious growth has 

 appeared, pour 2 to 3 cc. of a sterile -5 per cent caustic potash 

 solution, or of distilled water, into each tube. 



(2) Scrape the cultures off the surface of the agar-agar 

 into the alkaline solution or into the water. 



(3) Collect the various emulsions in a flask, and heat for 

 ten minutes in a water bath at 80 to 100 C. 



(4) Filter through a small Berkefeld filter into a sterilised 

 flask. 



