124 • APPENDIX. 



POTATO. 



Large, sound potatoes are thoroughly washed and 

 brushed with a scrubbing-brush, then pared and cut into 

 cylinders with a cork-borer. After paring, the potato 

 should be kept under water as much as possible to pre- 

 vent darkening. The cylinders are then cut diagonally so 

 that each produces two pieces of the general shape of a 

 solidified agar or serum slant. The pieces are then left 

 in cold, running water for several hours, after which they 

 are dropped, broad end down, into test-tubes containing 

 a small piece of glass rod or tubing at the bottom to keep 

 the potato out of the watery fluid which is produced by 

 sterilizing. Sterilize for twenty minutes at ioo° C. on 

 three successive days, or for fifteen minutes at no° C. 



NITRATE SOLUTION. 



A stock solution is prepared by dissolving 2 grams C. P. 

 potassium nitrate in 100 c.c. sterile distilled water. This 

 should be kept in the ice-chest. Five c.c. of this solution 

 and 1 gram peptone are added to 1 liter of tap-water. 

 The solution is brought to a boil, filtered, and tubed. 



Care must be taken that the stock solution does not 

 become reduced to nitrites or that nitrite is not present 

 in the original salt. Sterilize for fifteen minutes at 120 . 



PEPTONE SOLUTION. 



Ten grams peptone and 5 grams of salt are dissolved in 

 1 litre of water; the solution is boiled, filtered, tubed, and 

 sterilized for fifteen minutes at 120 C. 



