PREPARATION OF GLYCERIN POTATO 



27 



4. Transfer the pieces to a 5% solution of glycerin in 

 water for a further twenty-four hours only. 



5. Place in sterile tubes 

 prepared as follows: Select 

 extra large test tubes 1.5 

 to 2 cm. in diameter and 

 clean and dry them. Place 

 a small piece of absorbent 

 cotton or glass rod 0.5 cm. 

 X2.5 cm. in the bottom of 

 each. Plug with cotton 

 and sterilize in the usual 

 way. (Roux tubes need 

 only to be cleaned and 

 sterilized.) 



Just before introducing 

 the pieces of potato, add 

 about 1 c.c. of distilled water 

 to each tube, using a pi- 

 pette. The potato should 

 not touch the water. 



6. Sterilize by heating 

 at 100 G. on four successive 



days for twenty minutes 

 each day. 



FIG. 8. Potato Tubes. (Orig. 

 Northrup.) 



Caution: The time stated in 3 and 4 must be strictly adhered to, 

 else the potatoes will have to be discarded on account of contamina- 

 tion with resistant spore-forming organisms. 



REFERENCE 



SMIRNOW, M. R.: The value of glycerinated potato as a culture 

 medium. Cent. f. Bakt., II Abt., Bd. 41, p. 303. 



