62 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



be inert. Many bacteria belong to this group, which in- 

 cludes some of the udder cocci. Many of the most im- 

 portant pathogenic organisms are also inert in so far as 

 their effect on milk is concerned, notably the tubercle 

 bacillus, the bacillus of typhoid fever, paracoli or para- 

 typhus bacilli, and the diphtheria bacillus. The presence 

 of these harmful organisms is not indicated by any ap- 

 parent change in the milk. 



VARIATIONS IN NUMBER AND KIND OF BACTERIA 



Different samples of market milk may show the 

 greatest differences in the number and kind of bacteria 

 present. One sample may contain much fewer than 1000 

 bacteria per c.c. and another may contain four or five 

 million and even more. In one sample, the bacteria may 

 be largely of the inert forms and in another the bacteria 

 of the gas-forming group may predominate. Market 

 milk containing not more than 100,000 bacteria per c.c. 

 is considered of good quality. The limit for certified 

 milk is 10,000 bacteria per c.c. 



The kind or species of the bacteria must be considered 

 as well as the number. Generally, the smaller the num- 

 ber of bacteria present the better the milk, but there are 

 exceptions to this rule. A few pathogenic organisms 

 would be more harmful than a much larger number of 

 the common milk bacteria. Between the different groups 

 of the latter there are also important differences. Milk 

 containing a rather large number of bacteria the greater 

 proportion of which belong to the inert or lactic acid 

 groups is less objectionable than milk containing a 

 smaller number of bacteria with the greater proportion 

 belonging to the gas-f orming or peptonizing groups. On 

 the other hand, while milk containing a large percentage 



