NUTRIENT MEDIA AND METHODS OF CULTIVATION. 



121 



a long filament, and the subsequent development of bright oval 

 spores. It is necessary carefully to observe the minutest details 

 in order to maintain the cultivation pure. An excavated slide is 

 thoroughly cleaned, and then sterilised by being held with the 

 cupped side downwards in the flame of the Bunsen burner. A ring 

 of vaseline is painted round the excavation, and the slide is then 

 placed under a glass bell. Meanwhile a carefully cleansed cover- 

 glass is also sterilised by passing it through the flame, and should 

 be deposited on a sterilised glass plate. With a sterilised looped 

 needle, a drop of sterile broth is transferred to the cover-glass, 

 and this is inoculated by touching it with another sterilised needle 

 charged with the material to be examined, without disturbing 

 the form of the drop. It is quite sufficient just to touch the drop 



FIG. 48. DROP CULTIVATION. 

 (a) Drop of broth ; (6) layer of vaseline. 



instead of transferring a visible quantity of blood, juice, or growth, 

 as the case may be. The slide is then inverted and placed over the 

 cover-glass, so that the drop will come exactly in the centre of the 

 excavation, and is gently pressed down. On turning the slide over 

 again the cover-glass adheres, and an additional layer of vaseline 

 is painted round the edges of the cover-glass itself. The slide must 

 be labelled, and if necessary, placed in the incubator, and the results 

 watched from time to time. Instead of broth, liquid blood serum 

 may be employed in this form of cultivation. If it is required 

 to preserve the drop-cultivation as a microscopic preparation, the 

 cover-glass is gently lifted off and allowed to dry. Any vaseline 

 adhering to the cover-glass should be wiped off, and the cover-glass 

 can then be passed through the flame and stained in the usual manner. 

 Moist Cells. Unless drop-cultures are very carefully prepared 



