278 GENERAL MICROBIOLOGY 



Did straining have any effect on the numbers of organisms 

 present in the milk? What effect may it have? Is this 

 beneficial to the milk as a commercial product? 



9. In what way may the microscopic sediment test 

 explain the results obtained by plating milk before and after 

 straining? 



10. Make, stain and examine smears from the upper 

 surface of the cotton disk. What is the nature microscopic- 

 ally of the material retained by the cotton? How does this 

 smear compare qualitatively with that from the centri- 

 fuged sample? 



11. What is the nature of the dirt ordinarily found in 

 milk? How may its presence be eliminated? 



12. Give all results in full and draw any conclusions 

 permissible, Point out any practical applications. 



REFERENCES 



LOHNIS: Laboratory Methods in Agricultural Bacteriology, pp. 63-65. 

 JENSEN: Milk Hygiene, transl. by Pearson (1907), pp. 126-127. 

 MARSHALL: Microbiology, pp. 326-327. 

 ROSENAU: The Milk Question (1912), pp. 55-88. 

 ERNST: Milk Hygiene, transl. by Mohler and Eichhorn (1914), p. 

 182. 



EXERCISE 5. TO DETERMINE THE INFLUENCE OF 

 TEMPERATURE UPON THE KEEPING QUALITY OF 

 MILK; PITRE MILK COMPARED WITH MARKET 

 MILK 



One of the most important considerations in the pro- 

 duction of milk, either for factory use or for town or city 

 supply, is the temperature at which the milk is maintained. 

 The beneficial effects of scrupulous cleanliness in the pro- 

 duction of milk will be largely counteracted unless the milk 

 is cooled immediately after drawn and maintained at a 

 temperature too low for development of the bacteria 

 present. 



