16 PRACTICAL BACTERIOLOGY 



VI. THE HANGING DROP. 



1. Place directly in the middle of a clean cover-glass with the 

 sterilized platinum loop a minute drop of the fluid to be examined ; 

 if a semi-solid, a drop of sterile water, physiological salt solution, or 

 bouillon is first placed on the cover-glass and then inoculated. 



2. The edges of the circular cavity in the hanging-drop slide are 

 painted with a narrow strip of vaseline with a cameFs-hair brush. 



3. Reverse the slide and place it upon the cover-glass so that the 

 inoculated drop is exactly in the centre of the hollow chamber. 

 Apply gentle pressure when the cover-glass adheres to the slide by 

 means of the vaseline, forming an air-tight cavity. The preparation 

 is now turned upwards quickly (to prevent running of the drop) and 

 examined as follows : 



The convenient method of beginners, or those examining many 

 drop cultures, is that recommended by Nuttall, consisting of making 

 small rings upon the cover-glass with a mixture of lamp-black and 

 blood serum applied with a camePs-hair brush and a turn-table, and 

 passed in the usual manner through the flame. 



1. Cut off the light in the condenser with a narrow diaphragm 



about the size of a pin-head. 



2. Find the edge of the hanging drop with the low power and plain 



mirror. 



3. Regulate the Abbe condenser, and throw the light into the 



specimen. 



4. Place the illumination or light in the centre of the specimen by 



manipulating the mirror. 



5. Screw up the tube, remove the low power, and adjust the immer- 



sion lens. 



6. Increase the size of the diaphragm to about the size of a pea. 



7. Put a drop of immersion oil on the cover-glass. 



8. Screw down the tube with the coarse adjustment until the point 



of the lens touches the oil, and then screw back the tube 

 without breaking the oil connection. 



9. Screw down the tube again by means of the coarse adjustment 



until the object comes in view. 



10. Regulate the focus with the fine adjustment. 



11. If the field is not evenly illuminated, adjust the mirror without 



further removal. 



The hanging-drop method is used to study the morphobiological 

 characteristics of organisms, and the intravital phenomena connected 

 therewith. 



