HANGING-DROP PREPARATIONS 69 



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

 the edge of the cell, and the preparation is then complete and may 

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

 incubated 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 87. 



Anaerobic Hanging-drop Cultures. The growth and exami- 

 nation of bacteria in hanging-drops under anaerobic conditions 

 involve considerable difficulty, but may be carried out in 

 an apparatus devised by A 



Graham Brown (Fig. 35). 

 It consists of two brass 

 plates (a and a') which 

 can be approximated by 

 screws, and which have two 

 rounded apertures in their c 

 middle, f inch in diameter. 



: / 



These support two rubber f d e 



rings, an upper thinner FIG. 35. Graham Brown's chamber for anaerobic 



one (b) and a lower thick hanging-drops. 



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



one (a), their inner diame- 

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

 b and d is placed a stout cover-glass of suitable size (c) ; d is 

 separated from the plate a 1 by a square plate of glass e (a por- 

 tion of an ordinary glass slide for microscopical purposes does 

 well). Two small metal tubes / are inserted through the rub- 

 ber d. Method of use : Fix up the apparatus as shown above, 



