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/ 1 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. Isabel 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 /o 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^ of pure 

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

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

 nary agar. 



