25 



to a (loan dry room, strain carefully, and c-ool to iM)° ¥., if possible, to 

 prevent too rapid growth of bacteria. The aeration of milk before 

 cooling should be done, if at all, only in air comparatively free from 

 bacteria and never in the stable (reference No. 9, p. 55). After the 

 milk has })een cooled to 60° F. it should be covered to prevent evap- 

 oration and consetjuent thickening of layer of cream (reference No. 

 8, p. 17). 



8. Cleanliness in cheese factory. — Cleanliness in a cheese factory is 

 just as important as in the barn. Good milk can not be made into good 

 cheese in a dirty factory. The inside and outside of weighing can, 

 cheese vats, etc., nmst be kept strictly clean. The floors must be 

 scrubbed thoroughly (reference No. 8, p. 19). Sal soda is in many 

 cases a cheap substitute for soap, not only dissolving grease, but 

 neutralizing acids and loosening dirt. Everything possible must be 

 done to prevent any accumulation of dirt in corners. All cloth mate- 

 rials used must be thoroughly boiled at frequent intervals. All drains 

 should be kept disinfected (reference No. 8, p. 20). 



EXPERIMENT AND PRACTICE WORK, THIRD LECTURE. 



Tim.e required for experiments. — Four hours at least mil probably be 

 required to get the work started and much more will be needed to 

 become at all skillful. 



Apparatus required. — (1) 1 cubic centimeter pipettes inclosed in 

 glass tubes for sterilizing; (2) small flasks marked to hold 99 cubic 

 centimeters; (3) small homeopathic vials, some marked to hold 19 and 

 some 5 cubic centimeters; (4) absorbent cotton; (5) peptone-agar cul- 

 ture medium; (6) Petri dishes, and (7) test tubes. 



1. General outline of method used in determining the number of germs 

 in milk. — The method of finding out how many bacteria are present in 

 milk is based upon placing a small amount of milk upon a sterile sub- 

 stance which mil enable the bacteria to grow. After 24 to 36 hours 

 small spots appear and their number is greater or less according to the 

 number of bacteria in the milk (references No. 9, pp. 251-266, and 

 No. 11, p. 32). 



2. Sterilizing milk. — Determine the acidity of some milk and put 

 some in a half dozen test tubes and plug the tubes with absorbent 

 cotton. Then place in boiling water thirty minutes. Let them stand 

 at room temperature. At the end of four days determine the degree 

 of acidity in tube No. 1 ; at the end of eight days determine the acidity 

 in No. 2, and continue examining at intervals of four days until all 

 have been examined. Do not remove the cotton plug from any tube 

 until you are ready to examine at once. 



Sterilize a portion of some milk and then allow sterilized and unster- 

 ilized portions to stand uncovered at room teinperature. Examine 

 each day and notice when each coagulates. 

 25300— No. 166—06 i 



