AMOUNT AND KIND OF DIRT IN MILK 273 



tegrate the dust particles by stirring with a sterile glass 

 rod and agitating. Plate 1 c.c. in litmus lactose agar. 



4. Quantitative studies of barn air under various con- 

 ditions may be made according to Exercise 1, Air Micro- 

 biology. 



5. What advantage has litmus lactose agar over ordi- 

 nary agar in this exercise? 



What types of organisms are met most frequently under 

 A, B, C, D, E and F? How may this occurrence be ac- 

 counted for? 



Which sources furnish the greatest number of organisms? 

 From which sources are the greatest number of micro- 

 organisms most likely to enter milk? The most undesirable 

 types? Explain in each case. 



What sources of milk contamination have not been dis- 

 cussed under this exercise? Of what importance is each? 

 What is the simplest method in each case of preventing 

 contamination from the various sources mentioned above? 



6. Give your results in full and draw any conclusions 

 and make any practical applications possible. 



REFERENCES 



SAVAGE: The Bacteriological Examination of Food and Water (1914), 



pp. 90-91. 

 ERNST: Milk Hygiene, transl. by Mohler and Eichhorn (1913), pp. 



67-102, 125-131, 234-235. 



JENSEN: Milk Hygiene, transl. by Pearson (1907), pp. 70-82, 86-127. 

 MARSHALL: Microbiology, pp. 300-306. 



EXERCISE 4. TO INVESTIGATE THE AMOUNT AND 

 KIND OF DIRT IN MILK AND ITS RELATION TO THE 

 MICROBIAL CONTENT OF THE MILK 



Apparatus. Six sterile 1 c.c. pipettes; 99 c.c. dilution 

 flasks; six tubes sterile litmus lactose agar; six sterile 

 Petri dishes; sedimentation tubes, 10 c.c. capacity; balance; 

 centrifuge; clean slides; methylen blue, aqueous-alcoholic; 

 physiological salt solution; pneumatic or other type of 



