MILK 99 



this organism does not multiply in milk and so is of equal value 

 for byre and vended milk samples. The spores are present in 

 considerable numbers in cowdung. If the method of enumera- 

 tion described in this Chapter is adopted, o or I (i.e. all ten tubes 

 negative or only I positive) might be considered good, 2, 3, or 4 

 positive as unsatisfactory, and 5 or over positive as bad. 



The estimation of the sediment or dirt in milk is considered 

 by many workers to be a very valuable guide to the bacterial 

 contamination of milk. Since the bacteria which gain access to 

 milk are contained in particulate matter, generally in manure, 

 there is some justification for estimating the deposit in milk and 

 taking it as an index of the number of undesirable bacteria 

 \vhich have gained access to it. The test is also a non-multiply- 

 ing one, so is as valuable for vended as for byre milk samples. 

 The amount of sediment can also be fairly easily and quickly 

 estimated. 



The objections on the other hand are considerable and 

 important and are briefly that there is no definite relationship 

 between the amount of sediment and the number of bacteria, 

 that the sediment is only partially manurial, part being harmless 

 inorganic substances or substances natural to milk, and that 

 the amount is directly proportional to the efficiency of straining 

 rather than to the cleanliness precautions adopted. 



The last is the most important objection since straining 

 while it removes the larger dung-particles does not remove the 

 bacteria and makes the test of but little value. 



Acidity determinations are of no real value to estimate 

 bacterial contamination since there is no relationship between 

 the number of bacteria or B. coli and the degree of acidity. 



The detection of pathogenic bacteria in milk. 

 Apart from certain types of streptococci, the only pathogenic 

 organisms for which it is likely that milk will be required to be 

 examined are the bacilli of tuberculosis, diphtheria, and typhoid 

 fever. 



Examination for B. tuberculosis. Tubercle bacilli, when 

 present in milk, are frequently only in small numbers. It is 

 therefore of importance to examine a considerable amount of 



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