170 ' METHODS OF USING CULTURE MEDIA 



preferred for most "stab" cultures) are filled one-third full 

 of the medium while it is still fluid, plugged, sterilized 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. 117, Nos. 4 and 5). 



Fig. 118. — 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 solidifies 

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

 surface on which the bacteria are inoculated (Fig. 117, 

 Nos. 6 and 7). 



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

 cultures (Fig. 117, No. 8). Potatoes as "plate cultures" 

 have been referred to. Agar and gelatin are very largely 



