x DISINFECTION WITH GASES 129 



(ii.) Sternberg's method. 



This method is more convenient than Koch's method for 

 all practical purposes, and the results are more useful, 

 because the conditions of the experiment resemble more 

 closely those of practice. 



(1) Take five tubes containing 5 cc. of broth each, and 

 inoculate them with the bacillus of typhoid fever. 



(2) After twenty-four hours add to four of the tubes 

 respectively 5 cc. of carbolic acid solutions, of the following 

 strengths, 1 : 200, 1 : 100, 1 : 50, 1 : 20. The fifth tube 

 must be left for the purpose of control. 



(3) Place the tubes in the warm incubator for two to four 

 hours, or other periods of time. 



(4) Then make five subcultures in broth from these 

 five tubes (one or two platinum-loopfuls). 



(5) Keep them in the incubator at 38 -5 C. for several 

 days. 



Examine the tubes for growth from day to day. 

 (The carbolic acid solutions must be prepared with 

 sterilised water.) 



(C) DISINFECTANT ACTION OF GASES. 

 (a) Sulphur dioxide. 



(1) Dip strips of sterilised cloth in a fresh broth cul- 

 ture of Staphylococcus pyogenes aureus, place them in a 

 sterile Petri's capsule, and allow them to dry in the warm 

 incubator. 



(2) Fix up an apparatus in the fume cupboard to pre- 

 pare sulphur dioxide, as shown in the diagram (Fig. 1 4). 



K 



