FOOD 461 



2 . Mince a portion of the sample by the aid of sterile 

 scissors and forceps, and add the minced sample to 

 the bouillon in the flask to the extent of 20 grammes. 



3. Make an extract by standing the flask in the 

 incubator running at 42 C. (or in a water-bath regu- 

 lated to that temperature) for half an hour, shaking its 

 contents from time to time. Better results are ob- 

 tained if an electrical shaker is fitted inside the incu- 

 bator and the flask kept in motion throughout the 

 entire thirty minutes. 



Now every centimetre contains the bacteria washed 

 out from o.i gramme of the original food. 



4. Inoculate tubes of liquefied gelatine as follows: 



To tube No. i add i .o c.c. of the extract. 



2 add 0.5 c.c. of the extract. 



3 add 0.3 c.c. of the extract. 



4 add o. 2 c.c. of the extract. 



5 add o.i c.c. of the extract. 



Pour plates from these tubes and incubate at 20 C. 



5. Prepare a precisely similar set of agar plates and 

 incubate at 3 7 C. . 



6. Pipette 5 c.c. of the extract into a sterile tube, 

 heat in the differential steriliser at 80 C. for ten 

 minutes. 



7. From the heated extract prepare duplicate sets of 

 agar and gelatine plates and incubate anaerobically 

 in Bulloch's apparatusat 37 C. and 20 C. respectively. 



8. After three days' incubation examine the agar 

 plates both aerobic and anaerobic and enumerate 

 the colonies developed from spores (7), and from vege- 

 tative forms and spores (5), and calculate and record 

 the numbers of each group per gramme of the original 

 food. 



9. After seven days' incubation (or earlier if com- 

 pelled by the growth of liquefying colonies) enumerate 

 the gelatine plates in the same way. 



