62 



SOLID CULTIVATION MEDIA. 



Summary of Process for preparing Sterile Potatoes. 



Cleanse potatoes. 



Steep in one-half per cent, solution of corrosive sublimate for forty- 

 five minutes. 



Rinse with distilled water. 



Steam for thirty minutes at ioo° C. 



Divide with knives which have been previously heated red hot. 



Place in sterile bell jars, purified with one per cent, solution of 

 corrosive sublimate. 



Inoculation of Potatoes. 



40. Such potatoes should either be inoculated at once with seed 

 material, or allowed to stand under observation for four days before this 

 is done. In the former case the implanted 

 organisms have the start of any which may 

 have gained access during the processes of 

 preparation or of inoculation. In the latter, 

 if no reaction take place, one may be quite 

 sure that the soil to be inoculated is per- 

 fectly sterile. In inoculating sterile pota- 

 toes, as also the various other soils, for the' 

 growth of organisms subsequently to be 

 described, a platinum wire mounted upon 

 a glass rod (see Fig. 21) is used. This is 

 sterilised immediately before use by heating 

 it white hot in the flame of a Bunsen burner. 

 The upper part of the glass rod is also 

 heated. In a few seconds the wire is cool 

 enough to be used without damaging the 

 seed material, which it is to transfer to the 

 sterile potato surface. The wire, sterilised 

 and charged with a small quantity of the 

 seed material, is held in one hand ; wjth the 

 other the operator slowly raises the upper 

 glass bell at one side, so as just to allow of 

 the entrance of the wire. The end of the 

 wire is now rubbed gently upon the centre 



Fig. 21. — Platinum wires 

 used for making inoculations. 



a. Straight wire for inocu- 



lating gelatine, bread 

 paste, &c. 



b. Looped wire for liquids. 



c. Hooked wire for inocu- 



lating solidified blood 

 serum and potatoes. 



d. Bottle, with wadding on 



which glass rods rest. 



