STAINING OF FLAGELLA. I37 



the slide, as tbe organs of movement, which are ex- 

 tremely delicate, may easily be torn o£F. Tap water 

 is chosen because the bacteria are so extraordinarily 

 sensitive that they often cast off their flagella if 

 placed in distilled water. We now place small drops 

 of water upon a number of cover-glasses, which have 

 been sterilised and heated as before described (p. 91), 

 and with the platinum wire introduce into each of 

 them a minute quantity of the water on the slide 

 which contains the bacilli. The following precautions 

 must be most carefully taken if the experiments are 

 to succeed : — 



1. The cover-glasses mast be absolutely clean, in 

 which case the drop of water will spread itself out 

 evenly over the surface, and not run back or refuse to 

 adhere to any portions of it. The smallest particles of 

 dirt become stained during the following experiments, 

 and then may completely conceal the faintly stained 

 flagella. 



2. No trace of agar-agar should be transferred to the 

 preparation, or the result is the same as if the cover 

 glass were dirty. 



3. There must not be too many bacilli upon each 

 cover-glass, for they should be scattered, and the 

 distance between them should be greater than the 

 diameter of the bacilli themselves. 



The drop is now spread out upon the cover-glass, 

 and is allowed to dry in the air. The greatest care is- 



