PREPARATION OF NUTRIENT MEDIA. 79 



potato treated in the same way is placed in the 

 same damp chamber. The four halves are then 

 quite ready for inoculation. As an extra pre- 

 caution the left hand is again dipped in sublimate, 

 and one half of a potato is taken up between the 

 tips of the thumb and index fingers, care being 

 taken to avoid touching the cut surface. Holding 



FIG. 30. METHOD OF DIVIDING POTATOES. 



it with its cut surface vertical, a small portion 

 of the substance to be inoculated is placed on 

 the centre with a sterilised needle or ose. With 

 a sterilised scalpel the inoculated substance is 

 rapidly spread over the surface of the potato 

 with the flat of the blade to within a quarter of 

 an inch of the margin, and the potato is then as 



