234 METHODS OF CULTIVATION 



cover it with a small bell glass that has been rinsed 

 out with the same solution and not dried. 



4. Raise the bell glass slightly and smear sterile 

 vaseline around the rim of the metal cell by means of a 

 sterile spatula of stout platinum wire. 



5. Remove a clean cover-slip from the alcohol pot 

 with sterile forceps and burn off the alcohol; again 

 raise the bell glass and place the sterile cover-slip on 

 the blotting paper by the side of the hanging-drop slide. 



6. Remove a drop of the broth from the second 

 dilution tube with a large platinum loop; raise the 

 bell glass and deposit the drop on the centre of the 

 cover-slip. Sterilise the loop. 



7. Raise the bell glass sufficiently to allow of the 

 cover-slip being grasped with forceps, inverted, and 

 adjusted over the cell of the hanging-drop slide. Re- 

 move the bell glass altogether and press the cover-slip 

 firmly on to the cell. 



8. Either incubate and examine at definite intervals, 

 or observe continuously with the microscope, using 

 a warm stage if necessary (Fig. 53). 



(b) Solid Media. Observing precisely similar tech- 

 nique, a few drops of liquefied gelatine or agar from 

 the second dilution tube may be run over the surface 

 of the sterile cover-slip and a hanging-drop plate cul- 

 tivation thereby prepared. 



This method is extremely useful in connection with 

 the study of yeasts, when the circular cell on the 

 hanging-drop slide should be replaced by a rectangu- 

 lar cell some 38 by 19 mm., and the gelatine spread 

 over a cover-slip of similar size. After sealing down 

 the preparation, the upper surface of the cover-slip 

 may be ruled into squares by the aid of the grease 

 pencil or a writing diamond and numbered to facilitate 

 the subsequent identification of the colonies which are 

 observed to develop from solitary germs. 



