66 A MANUAL OF BACTERIOLOGY 



a sterilised glass ring ( j in. diam. x | in. high) to a 

 microscopic slide, which has been thoroughly cleaned 

 and sterilised (Fig. 25). The upper edge of the ring 

 is moistened with olive oil or vaseline ; and the cell is 

 covered over by means of a thin cover-glass, previously 

 sterilised by passing it through a Bunsen flame. 

 The surface of the sterilised cover-glass (A) contains 

 a drop of bouillon or other medium, along with the 

 microbes for examination. A drop or two of 

 sterilised water should be deposited at the bottom 

 of the cell ; i.e. upon the upper surface of the glass 

 slide. This arrangement forms a miniature damp 

 chamber, in which the growth of microbes may be 

 watched even under the highest powers. After the 

 examination of the cell and its contents, it may be 

 placed in an incubator until it is required again for 

 microscopical examination. 



To study the action of heat on drop cultures, the 

 warm stages of Schafer, Eanvier, Israel, Schultze, 

 Strieker, etc., are often used upon the fixed stage of 

 the microscope. 1 The action of various gases on 

 drop-cultures may be watched by a modification of 

 the glass cell as represented in Fig. 25. The gases 

 enter through B. The author has used this device 

 during his researches on the action of certain gases 

 on Bacillus tuberculosis. The action of the voltaic 

 current or discharges of faradaic electricity may be 

 observed by simple modifications of the drop- culture 

 cell. 



1 An excellent piece of glass apparatus is used by the Rev. 

 W. H. Dallinger, F.R.S., for ascertaining the thermal death 

 point of microbes. (See Proc. Roy. Soc., 1878.) 



