rcKSIl 



31 



held with the thumb and forefinger of the left hand. 

 With a potato knife held vertically, the outer edge of the 

 potato is pared circularly. Two horizontal sections, one 

 upper and a lower one, are now made and the clean, 

 sound core of the potato thus obtained is slipped into a 

 sterilized Esmarch dish. Each dish is thus supplied with 

 a clean potato section. The dishes are then placed in a 

 steam sterilizer and steamed for f to 1 hour. The pota- 

 toes will then be sterilized and cooked. 



The inoculation of the cold sterilized potato is made 

 in essentially the same way as in the ordinary potato 

 culture?. As each potato is in a small sterilized dish by 

 itself the risk of contamination is very small under care- 

 ful and rapid manipulation. 



LABORATORY WORK. Make dilution cultures of Micro- 

 coccus prodigiosus, using three of the Esmarch potato 

 dishes. 



Test-Tube Potato Cultures. These were introduced 

 independently and almost simultaneously by Bolton of 

 this country, Globig, of Germany and Roux of France. 

 In convenience and reliability of cultures, the method 

 leaves nothing to be desired. 



Clean, plug and sterilize about 6 or 8 large test-tubes 

 (| x (> inches). Also clean several large potatoes and 

 place them in boiling water or in steam sterilizer for about 

 j of an hour. By means of a cork-borer, having nearly 

 the diameter of the test tubes, punch out a number of 

 cylinders from the cooled potatoes. Place these cylinders 

 on a clean piece of paper, trim off the ends and then cut 

 each cylinder diagonally into two pieces. Into each of 

 the sterilized test-tubes place one of these pieces of pota- 

 toes with the circular end lowermost. Each tube then 

 contains a piece of potato having an inclined surface. 

 Now sterilize again in a steam sterilizer for about f to 1 

 hour. 



Instead of a cork borer an excellent substitute may 

 be obtained by cutting a test tube in two. By making 

 cylinders from previously boiled potatoes, the pieces in 



