HANGING DROPS. 



DEMONSTRATION IV. 



Examination of Bacteria unstained — Hanging Drops — 

 Hanging Drop Cultures. 



1. With a sterile loop remove a drop of the liquefied 

 gelatine culture of Staphylococcus pyogenes aureus, and 

 place on a cover glass. Invert this cover glass on a 

 slide. 



Examine with the ^^ oil-immersion lens, shutting 

 off nearly all the light; or examine, after removing the 

 Abb6 condenser, using the concave mirror and partially 

 closed diaphragm. 



2. Repeat this procedure, using a drop of the broth 

 culture of Bacillus proteus mirabilis. Slight motility 

 of the bacilli may be seen. 



3. Examine in the same manner a drop of putrefy- 

 ing urine (48 hours old). Large numbers of bacteria, 

 usually of several species, are seen. 



Hanging Drops. 

 Hanging drop preparations are made to study 

 motility of bacteria. Under the microscope we may 

 make out three kinds of movement: (a) Current move- 

 ment, where the bacteria move with the suspending 

 fluid. (6) Molecular or "Brownian " movement, where 

 the bacteria vibrate in the fluid, as do all solid particles 

 suspended in fluids. In this movement there is no 

 actual change in position of the bacterial cells, (c) 



