PREPARATION OF POTATOES. 93 



they are usually intended to be cut in half, and the 

 cultivation of the organisms is to be conducted upon the 

 flat surfaces of the sections. (Koch's original method.) 



This method requires some care to prevent contam- 

 ination during manipulation. The hand which is to 

 take up the potato from the bucket, which until now has 

 remained covered, is first disinfected in the sublimate 

 solution for ten minutes, the potato is then taken up 

 between the thumb and index finger and severed into 

 two by a knife which has just been sterilized in the free 

 flame until it is quite hot. The blade of the knife is 

 passed not quite through the potato, but nearly so. A 

 large glass culture-dish for the reception of the two 

 halves of the potato, having been disinfected for twenty 

 minutes with 1 : 1000 sublimate solution and then 

 drained of all the adherent solution, is at hand ready 

 for the bits of potato; the cover is removed, and by 

 twisting the knife gently the two halves of the potato 

 may be caused to fall apart in the dish and usually to 

 fall upon their convex surfaces, leaving the flat sec- 

 tions uppermost. The cover is placed upon the dish 

 and the potatoes are ready for inoculation. 



2. Preparation of potatoes for test-tube cultures. Method 

 of Bolton. 1 If the potatoes are to be employed for test- 

 tube cultures, one simply scrubs off the coarser particles 

 of dirt with water and a brush, and with a cork-borer 

 punches out cylindrical bits of potato which will fit 

 loosely into the test-tubes to be used. On each bit of 

 potato is then to be cut a slanting surface running from 

 about the junction of the first and second thirds of the 

 cylinder to the diagonally opposite end. These cylin- 



i Medical News, 1887, vol. i. p. 138. 

 5* 



