Bacterial Standards. 239 



many miles into town in a wagon, to be consumed within 24 hours 

 after it is produced. In like manner this second type of city can 

 always maintain a lower bacterial standard than a city where the 

 general milk supply is hauled by railroad long distances and is 

 several days old when consumed. In drawing conclusions as to 

 the relative efficacy of milk control in cities comparisons must be 

 made between cities of the same class. 



The commission deems it of the utmost importance that some 

 standard method should be adopted for estimating and comparing 

 the bacterial character of milks, since by this means only is it 

 possible to grade and classify milks and to enforce bacterial 

 standards. There is much diversity of opinion as to the best 

 method of valuing bacteria counts. The average of a series gives 

 results which are misleading about as frequently as otherwise. In 

 the average a single high figure may unduly overbalance a large 

 number of exceedingly low counts. There are objections to the 

 use of the "median" or middle number when the counts are ar- 

 ranged in order of size, for the reason that the middle figure does 

 not distinguish between two groups in one of which there may be 

 some very high counts above the median and in the other of which 

 there are none. The method of dividing results into groups as 

 recommended by the American Public Health Association, while 

 a step in the right direction, is cumbersome and does not clearly 

 indicate whether or not a milk conforms to a given bacterial 

 standard. 



The commission passed a resolution at its last meeting regard- 

 ing the number of bacterial tests necessary to determine the grade 

 into which a milk falls, as follows: 



That the grade into which a milk falls shall be determined bacteriologically by at 

 least five consecutive bacteria counts taken over a period of not less than one week nor 

 more than one month, and at least 80 per cent (four out of five) must fall below the limit 

 set for the grade for which the classification is desired. 



Laboratory Examinations for Bacteria. 



On the subject of laboratory examinations of milk for bacteria 

 the commission passed the following resolutions: 



1. That the interests of public health demand that the control of milk supplies, 

 both as to production and distribution, shall include regular laboratory examinations of 

 milk by bacteriological methods. 



2. That among present available routine laboratory methods for determining the 

 sanitary quality of milk the bacteria count occupies first place. 



3. That bacteriological standards should be a factor in classifying or grading milks 

 of different degrees of excellence. 



4. That in determining the grade or class of a raw milk the specimen taken for 

 bacteriological examination should be of milk as offered for sale. 



5. That there should be bacteriological standards for pasteurized milk which should 

 require laboratory examination of samples immediately before pasteurization as well as 

 of milk offered for sale. 



6. That the bacteria count of milk indicates its quality and history as it is modified 

 by contamination, handling, dirt, temperature, or age. A high count indicates the 

 necessity of investigation and inspection. 



