METHODS OF USING CULTURE MEDIA 183 



are to be preferred for most *'stab" cultures) are filled one- 

 third full of the medium while it is still fluid, plugged, ster- 

 ilized^ and allowed to cool in the vertical position. The 

 medium is then ''inoculated" with a straight platinum needle 

 by plunging this into the center of the surface down to the 

 bottom of the tube (Fig. 116, Nos. 4 and 5). 



Fig. 117.— Fermentation tubes. 1, filled ready for use; 2, shows a cloudy 

 growth and the development of gas in the closed arm. 



Agar and blood serum are frequently used in the form of 

 ''slope" or "slant" cultures. That is, the medium solidi- 

 fies with the tubes lying on their sides which gives a long, 

 sloping surface on which the bacteria are inoculated (Fig. 

 116, Nos. 6 and 7). 



Potato tubes are likewise used for "slant" or slope" 

 cultures (Fig. 116, No. 8). Potatoes as "plate cultures" 

 have been referred to. Agar and gelatin are very largely 



