74 METHODS OF CULTIVATION OF BACTERIA. 



The method of culture in fluid media is used to obtain 

 the soluble products of such anaerobes as the tetanus 

 bacillus. 



When it is desired to grow anaerobes on the surface of a 

 solid medium such as agar, tubes of the form shown in 



FIG. 25. Tubes for anaerobic cultures on the surface of solid media. 



Fig. 25, a and ^, may be used. A stroke culture having 

 been made, the air is replaced by hydrogen as just described, 

 and the tubes are fused at the constrictions. Such a 

 method is of great value when it is required to get the 

 bacteria free from admixture of medium, as in the case of 

 staining flagella. 



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. 26. In A 

 there is ground out on one surface a hollow having a 

 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 



