122 BACTERIOLOGY. 



they are liable to dry up, if kept for examination for several days. 

 Many therefore prefer employing a moist cell, of which there are 

 several different forms in use. 



The drop-culture slide may be converted into a moist cell 

 by having a deep groove cut round the circumference of the con- 

 cavity. This groove is filled with sterilised water by means of a 

 pipette. A ring of vaseline is painted with the camel's-hair brush 

 outside the groove, and the cover-glass, with the drop -cultivation, 

 is inverted and placed over the concavity. This form is very useful, 

 as the slide can be easily cleansed and effectually sterilised by 

 holding it in the flame of the Bunsen burner. 



A very simple form of moist cell recommended by Schafer 



FIG. 49. SIMPLE METHOD OF FOKMING A MOIST CELL. 



may be used in some cases, but possesses the disadvantage of not 

 admitting of sterilisation by heat. A small piece of putty or 

 modelling wax is rolled into a cord about two inches long and J inch 

 thick. By uniting the ends a ring is formed, which is placed on the 

 middle of a clean glass slide. A drop of water is placed in the 

 centre of the ring, and the cell roofed in by applying a cover-glass. 



A cell somewhat similar in form, which has the advantage of 

 permitting of thorough cleansing, may be constructed by cementing 

 a glass ring with flat surfaces to an ordinary slide. Vaseline is 

 applied with a camel's-hair brush to the upper surface of the ring, 

 and one or two drops of water placed with a pipette at the bottom 

 of the cell. The cover-glass, with the preparation, is then inverted 

 over the cell and gently pressed down upon the glass ring. The 

 vaseline renders the cell air-tight, and, to a certain extent, fixes 

 the cover-glass to the ring. 



