70 METHODS OF CULTIVATION OF BACTERIA. 



MISCELLANEOUS METHODS. 



Hanging-drop Cultures. It is often necessary to observe 

 micro-organisms alive, either to watch the method and rate 

 of their multiplication, or to investigate whether or not they 

 are motile. This is effected by making hanging- drop 

 cultures. The method in the form to be described is only 

 suitable for aerobes. For this special slides are necessary. 

 Two forms are in use and are shown in Fig. 25. In A 

 there is ground out on one surface a hollow having a 



FIG. 25. 



A. Hollow ground slide for hanging-drop cultures shown in plane and section. 

 B. Another form of slide for similar cultures. 



diameter of about half an inch. That shown in B explains 

 itself. The slide to be used and a cover-glass are sterilised 

 by hot air in a Petri's dish, or simply by being heated in a 

 Bunsen and laid in a sterile Petri to cool. In the case of 

 A, one or other of two manipulation methods may be 

 employed, (i) If the organism be growing in a liquid 

 culture, a loop of the liquid is placed on the middle of the 

 under surface of the sterile cover-glass, which is held in 

 forceps, the points of which have been sterilised in a Bunsen 

 flame. If the organism be growing in a solid medium, an 



