54 METHODS OF CULTIVATION OF BACTERIA. 



FIG. 9. Potato jar. 



with i-iooo corrosive sublimate, and a piece of circular 



filter paper, moistened with the same, is laid in its bottom. 



On this latter are placed four 

 sterile watch glasses. Two 

 firm, healthy, small, round 

 potatoes, as free from eyes as 

 possible, and with the skin 

 whole, are scrubbed well with 

 a brush under the tap and 

 steeped for two or three hours 

 in i- 1 ooo corrosive sublimate. 

 They are steamed in the 



Koch's steriliser for thirty minutes or longer, or in the 



autoclave for a quarter of an hour. 



When cold, each is grasped between 



the left thumb and forefinger (which 

 have been sterilised with 

 sublimate) and cut 



i i i i n -1 FIG. 10. Cylinder of 



through the middle with potato cut obliqu } ely 



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 surfaces, 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, 

 introduced by Ehrlich, is the best means of 

 utilising potatoes as a medium. A large, long 

 potato is well washed and scrubbed, and 

 Ehrlich's peeled with a clean knife. A cylinder is then 

 ^ orec ^ ^ rom * ts mtei 'i r w i tn an a ppl corer or 

 a l ar e C01 "k 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 



FIG. ii. 



