MILK HYGIENE 123 



cities which have established a numerical standard in refer- 

 ence to the bacterial content of milk, it is desirable to have 

 some method by which it can quickly and easily be deter- 

 mined whether or not a sample of milk exceeds the estab- 

 lished standard. The analyst does not care to know the exact 

 number of organisms present, but merely whether the milk 

 is good, fair, or poor, with reference to the standard adopted. 



The smear prepared from the milk for determination of 

 the number of leucocytes present will serve for this purpose. 

 The average number of bacteria per field of the oil-immersion 

 lens is determined by counting those appearing in a number 

 of fields. From the average per field and the areas of field 

 and smear the number of bacteria per cubic centimeter of 

 milk may be calculated. Each diplococcus or diplobacillus, 

 each chain or clump of organisms, should be counted as one, 

 since such aggregations will usually produce but one colony 

 on the plate cultures. The legal standard always refers to the 

 number of organisms as determined by some method of plating. 



The value of this method depends much on the experience 

 of the analyst. With considerable experience it is certain 

 that in many cases it is possible to determine whether a 

 given sample falls below or greatly exceeds the standard. 

 Standards of this character, however, should not be inter- 

 preted too strictly. They serve as admirable aids in milk con- 

 trol, inasmuch as the inspector is thus able to concentrate 

 his attention on those cases which are designated as suspi- 

 cious by the laboratory analysis. Where direct tests show 

 a perfectly normal condition, plating is unnecessary, and 

 only the questionable samples need be further examined. 

 The exact counting is not necessary, a rapid glance over the 

 preparation enabling the experienced analyst to judge of the 

 quality of the milk. The examination also gives the analyst 



