36 



jecting above the frame of the cylindrical knife. All of the 

 skin must be removed. Wash the potato cylinders in cold, 

 running water for some 5 minutes (a longer time is prefer- 

 able) and place them in test tubes of the proper .size (large 

 or small according to size of cutter used), and add about i 

 c.c. of water to each tube. Sterilize them by discontinuous 

 boiling or steaming for 20 minutes each day for three con- 

 secutive days. Wipe, label, and store in locker. 



§ 48. Preparation of milk for a culture medium. 

 Place about 100 c.c. of fresh milk in a beaker in the ice box 

 and allow it to stand for from 10 to 15 hours. Then care- 

 fully remove the cream. It is well to filter the milk through 

 a thin layer of absorbent cotton to remove any masses of 

 cream. The reaction should be tested and if strongly acid 

 it should be rejected or made 1.5% acid to phenolphthaleni 

 by the addition of n/i sodium hydrate. Distribute the skimmed 

 milk in small test tubes (7 c.c. in each) and sterilize by dis- 

 continuous steaming in the same manner and for the .same 

 length of time as the potatoes. I,abel and store in locker. 



§ 49. Preparation of litmus milk for a culture medi- 

 um. This is prepared the same as the milk medium with the 

 addition of enough of an aqueous solution of litmus to impart 

 a decidedly blue color to the milk. Sterilize label and store 

 the .same as the milk. The litmus solution will be furnished. 



§ 50. Preparation of glucose agar. Prepare 100 c.c. of 

 agar (§ 16). Reserve one half of it for glycerine agar and 

 to the other half add i % glucose. Dissolve the powdered 

 glucose in about 5 c.c. of boiled, hot water before adding it 

 to the liquid agar. After thoroughly mixing distribute it 

 in small sterile test tubes. Sterilize, label, and .store the 

 same as ordinary agar. 



§ 51. Preparation of glycerine agar. Take the balance 

 of the agar prepared above (§ 50) and add 5^0 of pure 

 glycerin. Thoroughly mix it with the liquid agar, after which 

 distribute it in tubes. Sterilize, label, and store as ordi- 

 nary agar. 



