8o MICROSCOPICAL EXAMINATION OF BACTERIA 



tides of solid matter (including bacteria), when sus- 

 pended in a fluid, will always show a vibratory move- 

 ment affecting the entire field, but never altering the 

 relative positions of the bacteria. (Cocci exhibit this 

 movement, but with the exception of the Micrococcus 

 agilis, the cocci are non-motile.) 



(6) Streaming movement. This is due to currents 

 set up in the hanging drop as a result of jarring of the 

 specimen or of evaporation, or to the fact that the 

 cover-slip is not perfectly level, and although the 

 relative positions of the bacteria may vary, still the 

 flowing movement of large numbers of organisms in 

 some one direction will usually be sufficient to demon- 

 strate the nature of this motion. 



(c) Locomotive movement, or true motility, is deter- 

 mined by observing some one particular bacillus chang- 

 ing its position in the field independently of, and in a 

 direction contrary to, other organisms present. 



When the examination is completed and the specimen 

 finished with, the " fresh specimen " i. e., the slide with 

 the cover-slip attached must be dropped into the 

 lysol pot. In the hanging-drop specimen, however, 

 the cover-slip only is infected, and this may be raised 

 from the ring cell by means of forceps and dropped 

 into the disinfectant. 



Permanent Staining of the Hanging-drop Specimen. 

 Occasionally it is necessary to fix and stain a hanging- 

 drop preparation. This may be done as follows : 



1. Remove the cover-slip from the cell by the aid of 

 the forceps. 



2. If the drop is small, fix it by dropping it face 

 downward, whilst still wet, on to the surface of some 

 Gulland 's solution or corrosive sublimate solution (vide 

 page 82) in a watch-glass. If the drop is large, place 

 it face upward on the rubber mat, cover it with an 

 inverted watch-glass, and allow it to dry. Then fix 

 it in the alcohol and ether solution (vide, page 82) . 



