HANGING-DROP CULTURES 233 



two hours) . This evaporates the water of condensation 

 and gives the medium a firm, dry surface. 



4. On removing the plates from the incubator close 

 each dish and place it still upside 



down on the laboratory bench. 



5. Inoculate the plates in series of 

 three, as described for gelatine sur- 

 face plates 3-8. FlG> ing sur . 



face plate of agar. 



Hanging=drop Cultivation. 



Apparatus Required. 



Hanging drop slides. 



Caver-slips. 



Section rack (Fig. 75). 



Blotting paper. 



Bell glass to cover slides. 



Original culture. 



Tubes of broth, or liquefied gelatine or agar. 



Forceps. 



Platinum loop. 



Bunsen burner. 



Grease pencil. 



Sterile vaseline. 



Lysol. 



(a) Fluid Media. 



1. Prepare first and second dilutions of the inoculum 

 as directed for plate cultivations (vide pages 228-229, 

 sections 4 to 6) , substituting tubes of nutrient broth 

 for the liquefied gelatine. 



2. Sterilise a hanging-drop slide by washing thor- 

 oughly in water and drying, then plunging it into a 

 beaker of absolute alcohol, draining off the greater 

 part of the spirit, grasping the slide in a pair of forceps, 

 and burning off the remainder of the alcohol in the 

 flame. 



3 . Place the hanging-drop slide on a piece of blotting 

 paper moistened with 2 per cent, lysol solution and 



