LIQUID MEDIA. 95 



has already been referred to as a particularly in- 

 structive one. It enables us to study many of the 

 changes which take place during the life history of 

 micro-organisms. This is illustrated, for example, 

 by the anthrax bacillus, where we can watch the 

 gradual growth of a single bacillus into a long 

 filament, and the subsequent development of bright 

 oval spores. It is necessary carefully to observe 

 the minutest details 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. Mean- 

 while a carefully cleansed cover-glass is also 

 sterilised by passing it through the flame, and 

 should be deposited on the plate of blackened glass. 

 With a sterilised ose a drop of sterile bouillon is 

 transferred to the cover glass, and this is inoculated 

 by touching it with a sterilised needle charged with 

 the material without disturbing the form of the drop. 

 It is quite sufficient just to touch the drop instead 

 of transferring a visible quantity of blood, juice, or 

 growth, as the case may be. The slide is then in- 

 verted and placed over the cover-glass, so that the 

 drop will come exactly in the centre of the excava- 

 tion, 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 



