108 BACTERIOLOGY. 



five minutes. On the second and third days the steril- 

 ization is repeated for fifteen to twenty minutes each day. 

 They must not be removed from the sterihzing bucket 

 until sterilization is complete, when they are ready for 

 use. When prepared in this way they are usually in- 

 tended 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 in 

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

 flame until it is quite hot. The knife is passed not 

 quite through the potato, but nearly so. A large glass 

 culture-dish for the reception of the halves of the 

 potato, having been disinfected for twenty minutes with 

 1 : 1000 sublimate solution and then drained of all ad- 

 herent solution, should be at hand ready for the potato ; 

 the cover is removed, and by twisting the knife gently 

 the halves of the potato may be caused to fall apart in 

 the dish and usually to fall upon their convex surfaces, 

 leaving the flat sections uppermost. The cover of 

 the dish is replaced and the potatoes are ready for 

 inoculation. 



2. Preparation of potatwx for text-tube ciilturef!. Method 

 of Bolton} If the potatoes arc to be employed for test- 

 tube cultures, one simply scrubs oif the coarser particles 

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

 punches out cylindrical bits of potato which will fit 

 1 Medical News, vol. i, of 1887, No. 12, p. 318. 



