64 METHODS OF CULTIVATION OF BACTERIA 



the bouillon. The cover is then carefully lowered over the cell 

 on the slide, the drop not being allowed to touch the wall or the 

 edge of the cell. The edge of the cover-glass is covered with 

 vaseline, and the preparation is then complete and may be 

 placed under the microscope. If necessary, it may be first in- 

 cubated and then examined on a warm stage. (2) The sterile 

 cover-glass is placed on a sterile plate (an ordinary glass plate 

 used for plate cultures is convenient). The drop is then placed 

 on its upper surface, the- details being the same as in the last 

 case. The edge of the cell in the slide is then painted with 

 vaseline, and the slide, held with the hollow surface downwards, 

 is lowered on to the cover-glass, to the rim of which it of course 

 adheres. The slide with the cover attached is then quickly 

 turned right side up, and the preparation is complete. 



In the case of B the drop of fluid is placed on the centre of 

 the table x. The drop must be thick enough to come in contact 

 with the cover-glass when the latter is lowered on the slide, and 

 not large enough to run over into the surrounding trench y. 

 The cover-glass is then lowered on to the drop, and vaseline is 

 painted along the margin of the cover-glass. The method of 

 microscopic examination is described on page 85. 



Anaerobic Hanging-drop Cultures. The growth and examination of 

 bacteria in hanging-drops under anaerobic conditions involve consider- 



FIG. 28. Graham Brown's chamber for anaerobic hanging-drops. 

 (A portion of one edge of upper plate is shown cut away.) 



able difficulty, but may be carried out in an apparatus devised by 

 Graham Brown (Fig. 28). It consists of two brass plates (a and a') 

 which can be approximated by screws, and which have rounded 

 apertures in their middles f in. in diameter. These support two rubber 

 rings, an upper thinner one (b) and a lower thick one (d), the inner 

 diameters being the same as that of the apertures in the plates. Between 



