254 



METHODS OF ISOLATION 



sterile teat-pipette deposit a small drop of sterile water 

 in the centre of each of the nine divisions. 



c. With the sterilised platinum spatula raise one of 

 the marked colonies from the " plate 3 " and transfer it 

 to the first division in the ruled plate and emulsify it 

 in the drop of water awaiting it. Repeat this process 

 with the remaining colonies, emulsifying a separate 

 colony in each drop of water. 



(C) Preliminary Differentiation of Bacteria. 



a. Prepare a cover-slip film preparation from each 

 drop of emulsion in the " stock dish" and number to 



correspond to the division 

 from which it was taken. 

 Stain by Gram's method. 



b. Examine microscop- 

 ically, using the oil immersion 

 lens and note the numbers of 

 those cover-slips which mor- 

 phologically and by Gram re- 

 sults appear to be composed 

 FIG. i 39 .-Dia g ram for stock of different species of bac- 

 P late - teria. 



(D) Preparing Isolation Subcultures. 



a. Inoculate an agar slope and a broth tube from the 

 emulsion in the stock dish corresponding to each of 

 these specially selected numbers. 



b. Ascertain whether the cover-slips from the nine 

 emulsions in the stock dish include all the varieties 

 represented in the cover-slip film preparation made from 

 the original mixture before plating. 



c. If some varieties are missing prepare a second 

 stock dish from other colonies on plate 3, and repeat 

 the process until each morphological form or tinctorial 

 variety has been secured in subculture. 



d. Place the stock dishes in the ice chest to await the 



