POTATOES AS CULTURE MEDIA. 



FIG. 9. Potato jar. 



steamer and steamed in the Koch's steriliser for thirty 

 minutes or longer. When cold, each is grasped between 

 the left thumb and forefinger 

 (which have been sterilised with 

 sublimate) and cut through the 

 middle with a sterile knife. It 

 is best to have the cover of the 

 jar raised by an assistant, and 

 to perform the cutting beneath 

 it. Each half is put in one of 

 the watch glasses, the cut sur- 

 faces, which are then ready 

 for inoculation with a bacterial growth, being uppermost. 

 Smaller jars, each of which holds 

 half of a potato, are also used in the 

 same way and are very convenient. 



(b} By Slices in Tubes. 

 This method, intro- 

 duced by Ehrlich, is the 

 best means of utilising 



potatoes as a medium. A large, long potato is 

 well washed and scrubbed, and peeled with a 

 clean knife. A cylinder is then bored from its 

 interior with an apple corer or a large cork 

 borer, and is cut obliquely, as in Fig. 10. 

 Two wedges are thus obtained, each of which 

 is placed broad end down in a test-tube of 

 special form (see Fig. n). In the wide part 

 at the bottom of this tube is placed a piece of 

 cotton wool, which catches any condensation 

 water which may form. The wedge rests on 

 the constriction above this bulbous portion. 

 The tubes, washed, dried, and with cotton ^_EhrHch's 

 wool in the bottom and in the mouth, are tube contain- 

 sterilised before the slices of potato are in s piece of 

 introduced. After the latter are inserted, the pot 

 tubes are steamed in the Koch steam steriliser for one 

 hour. An ordinary test-tube may be used with a piece 



FIG. 10. Cylinder 

 of potato cut obliquely. 



