THE RELATION OF MICROORGANISMS TO MILK. 



3 2 7 



do not want milk that is sour or has unpleasant flavors and odors. In 

 order to sell his milk, therefore, the milkman must avoid the presence 

 of these undesirable conditions, and in proportion as he recognizes the rela- 

 tion between germ life and the quality of his product, will he pay attention 

 to the presence and development of microorganisms in his milk. In 

 like manner, the presence or absence of dirt contamination is important 

 from the commercial standpoint since it bears a relation to the bacterial 

 count, and, therefore, affects the keeping properties of the milk. Under 

 normal conditions there is a fairly direct relation between the amount of 

 visible or insoluble dirt and the number of bacteria found in any given 

 lot of fresh milk. This relation may be shown by the following samples 

 taken from four different milk producers: 



This relation does not always hold for the reason that a gram of one 

 kind of dirt may contain infinitely more organisms than an equal amount 

 of some other kind. The difference in the solubility of various forms 

 of dirt always causes apparent discrepancies in this normal relation. In 

 the majority of cases, however, the relation shown in the above examples 

 will hold reasonably true in the case of fresh milk. There is also a general 

 relation between the number of bacteria in fresh milk and the length 

 of time it will keep before souring and curdling. In this case the relation 

 is in inverse ratio, the smaller the initial contamination, the longer the 

 keeping time, and vice versa. This relation is also shown in the table 

 given above. There are many irregularities, however, in this relation 

 because of differences in the flora of fresh milk. It may frequently 

 happen that a sample of milk containing a relatively high number of 

 organisms will not sour as quickly as another sample with a smaller 

 original germ content. The associative action of the different species 



