APPENDIX III 



A METHOD BY WHICH CELLS CAN BE EXAMINED MICROSCOPICALLY 

 BETWEEN A COVER-GLASS AND A JELLY-FILM WITHOUT 

 THE FORMER EXERTING ANY PRESSURE ON THEM. (A 



"HANGING DROP" PREPARATION WITH THE JELLY METHOD) 



Two round cover-glasses are required. One should have a diame- 

 ter of half an inch, the other of seven-eighths of an inch. The 

 jelly from which the film is to be prepared is boiled and a drop 

 of it run on to a slide. Immediately, before the jelly has had 

 time to set, the small cover-glass is allowed to fall flat on the 

 centre of the jelly-film on the slide. Since the jelly is not set, 

 the cover-glass sinks into but not actually through it. The film 

 with the cover-glass embedded in it is allowed to set for about five 

 minutes. One needle is then placed vertically against one edge 

 of the small cover-glass embedded in the jelly, and the point of 

 another needle is inserted under the opposite edge of the cover- 

 glass. By a jerk of this needle the embedded cover-glass is lifted 

 out of the jelly, when it will be found that a shallow circular 

 depression exactly corresponding to the cover-glass is left in the 

 jelly-film. The base and sides of the depression will, of course, 

 be composed of jelly. The cells to be examined are placed in 

 citrate solution on the large cover-glass, which is inverted and 

 allowed to fall flat over the depression in the film. By this 

 means the large cover-glass is resting on the raised sides of the 

 depression, but the cells are in the depression. They can now 

 be made to absorb substances from the jelly, but the cover-glass 

 does not press them into it unless the cells are very large. This 

 method is useful for the in-vitro staining of motile bacteria, try- 

 panosomes, etc. 



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