64 PRACTICAL BACTERIOLOGY 



3. Remove both cotton plugs, and hold between third and fourth 

 and fourth and fifth fingers respectively of the left hand. 



4. Pass a sterilized platinum loop into the original tube without 

 touching the sides, and transfer one loop of material into the second 

 tube, using similar precautions. 



5. Heat the necks of both tubes in the flame, and scorch both 

 plugs before returning them. 



CXVIII. THE QUANTITATIVE PLATE CULTURE 

 METHOD. 



This method is used to determine the number of bacteria in a 

 given quantity of Material. Fluids are examined as follows : 



1. Transfer with a sterilized capillary pipette, y^ c.c. to 1 c.c. 

 of the material into 10 c.c. of liquefied sterilized gelatine, and mix. 



2. Another tube containing 10 c.c. of liquefied gelatine is in- 

 oculated in a similar manner. 



3. Pour the contents of the tubes on plates, as in the ordinary 

 plate method ( 108), or into Petri-dishes previously sterilized, and set 

 on one side for from twenty-four hours to seven days. 



When the colonies have developed, the exact number is ascer- 

 tained with the Wolff hugePs Counting Apparatus (see Fig. 13). ''Roll 

 cultures can also be used.'' 



'Solid Material '' is first reduced in a sterile mortar (see Favus 

 Crusts Method, 109, process No. 2), with 5 or 10 c.c. of sterile 

 bouillon, or physiological salt solution, and then tested as above. 



CXIX. METHODS OF CULTIVATING ANAEROBIC 

 BACTERIA. 



Anaerobic organisms are characterised by their inability to grow 

 in the presence of oxygen, and many devices are employed for the 

 exclusion of oxygen from the cultures. 



The preparation of suitable media and cultivation of anaerobic 

 bacteria require skill and knowledge of bacteriological technique. 



CXX. KOCH'S METHOD. 



Inoculate a gelatine plate, and cover the inoculated surface with a 

 thin piece of sterilized isinglass; organisms growing beneath this 

 plate are supposed to grow without oxygen. 



