94 



VETERINARY BACTERIOLOGY 



NON-LIQUEFIABLE MEDIA 



Potato. Cylinders are cut from potatoes by means of an apple- 

 corer or special potato borer. These are divided by a diagonal 

 longitudinal cut such that each half has one long sloping surface. 

 It is well to soak in running water for a few hours to prevent 

 their turning dark when sterilized. They are placed with the 

 sloping surface up in test-tubes with a bit of saturated absorbent 

 cotton in the bottom, or in special potato tubes. The latter 

 are tubes constricted a short distance from the bottom. The 

 bulb thus formed is filled with water and the potato rests on the 

 constriction above. This device enables one to keep the potatoes 



Fig. 52. Preparation of potato tubes: a, Potato cylinder cut diagonally; 6, 

 side view in tube; c, front view. 



moist for considerable periods. They are sterilized in the auto- 

 clave for fifteen minutes at 120. 



Other Vegetable Media. Carrots and other vegetables may 

 be prepared in the same manner as potato. 



Blood-serum. Solidified blood-serum has been found to be 

 essential to the growth in the laboratory of certain of the patho- 

 genic bacteria. It is best to avoid all the initial contamination 

 of the serum possible, as it is difficult, by the methods used in 

 sterilization, to rid the medium of all the spore producers when 

 they are present in considerable numbers. The blood, usually 

 from beef, is allowed to clot, and the clear, straw-colored serum 

 removed. A clear, solidified serum may be prepared by heating 



