142 BACTERIOLOGICAL CHEMISTRY LESSON 



(2) Place them in the water bath at 70 C. for fifteen 

 minutes. 



(3) Filter the sterilised broth cultures through a sterile 

 Berkefeld filter into a sterile flask. 



(d) " Intracellular " poisons. 



(1) Prepare ten agar-agar streak cultures of the Bacillus 

 prodigiosus, and keep them at 22 C. for twenty-four to 

 forty-eight hours. The whole surface of the agar-agar 

 should be uniformly inoculated. 



(2) To each tube add 10 cc. of sterile *6 per cent saline 

 solution, and with a stout platinum needle carefully scrape 

 the culture off the agar-agar into the salt solution, so as to 

 prepare suspensions of the bacilli. 



(3) Pour the liquid contents of the tubes into a small 

 flask. 



(4) Heat the flask and its contents in a water bath at 

 65 to 70 C. for fifteen minutes. 



(e) Filtered intracellular poisons. 



Proceed as above, but conclude by filtering the sterilised 

 contents of the flask through a sterile Berkefeld filter into 

 a sterile flask. 



In every case the solution, after sterilisation by heat or filtra- 

 tion, must be tested by inoculating from it two agar-agar tubes 

 (streak cultures). 1 



1 If the agar-agar tubes show any growth, the solutions must be 

 sterilised again, by heat or nitration, as the case may be. 



