250 METHODS OF ISOLATION 



either the first or the third method will be found most 

 convenient, affording as each of them does an opportun- 

 ity for the simultaneous isolation of several or all 

 of the varieties of bacteria present in a mixture. 



1. Surface Plate Cultivations. 



(a) Gelatine (vide page 164). 



(b) A gar (vide page 167). 



(c) Alkaline serum agar (vide page 211). 



These plates are prepared in a manner precisely 

 similar to that adopted for nutrient gelatine and 

 agar surface plates (vide pages 231-233). 



(d) Serum Agar. 



1. Melt three tubes of nutrient agar, label them i, 2, 

 and 3, and place them, with three tubes of sterile 

 fluid serum, also labelled la, 20,, and 30, in a water-bath 

 regulated at 45 C. ; allow sufficient time to elapse for 

 the temperature of the contents of each tube to reach 

 that of the water-bath. 



2. Take serum tube No. la and agar tube No. i. 

 Flame the plugs and remove them from the tubes 

 (retaining the plug of the agar tube in the hand) ; 

 flame the mouths of the tubes, pour the serum into the 

 tube of liquefied agar and replace the plug of the agar 

 tube. 



3. Mix thoroughly and pour plate No. i secundum 

 artem. 



4. Treat the remaining tube of agar and serum in a 

 similar fashion, and pour plates Nos. 2 and 3. 



5 . Dry the serum agar plates in the incubator running 

 at 60 C. for one hour (see page 232). 



6. Inoculate the plates in series as described for 

 gelatine surface plates (page 231). 



(e) Blood Agar, Human 



i . Melt a tube of sterile agar and pour it into a sterile 

 plate; let it set. 



