94 BACTERIOLOGY. 



ders of potato are now to be left in running water over 

 night, otherwise they will be very much discolored by the 

 sterilization to which they are to be subjected. At the 

 end of this time they are placed in previously prepared 

 test-tubes, one piece in each tube, with the slanting sur- 

 face up, the cotton plugs of the tubes replaced, and they 

 are then to be sterilized in the steam for fifteen to 

 twenty minutes on each of three successive days. 



Or the entire sterilization may be accomplished in 



the autoclave, with the steam under a pressure of one 



atmosphere, by a single exposure of twenty 



Fig. 18. ^q twenty-five minutes. When finished 



hey have the appearance seen in Fig. 18, 



xcept that there is no growth upon the 



urface as is shown in the cut. 



For some purposes potatoes may be ad- 

 vantageously peeled, sliced into disks of 

 ibout 1 cm. in thickness, and placed in 

 I mall glass dishes provided with covers, 



imilar to the ordinary Petri dishes. The 

 lish and its contents are then sterilized by 

 team in the usual way (method suggested 

 \ l)y von Esmarch). By this jjlan a relatively 

 I large area for cultivation is obtained. 

 I Potatoes may also be boiled, or steamed, 



ind mashed, and the mass placed in covered 

 I lishes, test-tubes, or flasks, and sterilized. 



■— ^ By this method one obtains in the mass a 



Potato in test- . . 



tube. mean or the composition or the several pota- 



toes, or bits of potatoes, used in making it, 

 an advantage where uniformity is desired. 



Care must be given to the sterilization of potatoes, 

 because they always have adhering to them the organ- 



