20 



A. P. H. A. MILK ANALYSIS 



The simplest form of verification for 

 official plate count in the case of raw 

 milk is to make a count from the same 

 sample of milk by direct microscopic 

 examination, and vice versa. If the 

 counts found from the second examina- 

 tion are such that they are readily 

 understandable under the known con- 

 ditions, a very large part of the un- 

 certainty existing in regard to the 

 first count is eliminated at once. 

 Under other conditions it meCy be 

 found advantageous to verify the rou- 

 tine plate counts by making plate 

 counts in which additional dilutions, 

 or plates are used. Likewise more 

 careful microscopic counts may be 

 obtained either by examining duplicate 

 preparations from the same sample 

 of milk, or by making a more careful 

 examination of the original preparation 

 than that made for routine purposes. 



If procedures of this sort were more 

 common in bacteriological laboratories, 

 control officials would have much 

 firmer ground upon which to defend 

 their actions in court if necessary. 



(e) sediment test 



Because much of the dirt that appears 

 as a visible and insoluble sediment in 

 milk is accompanied by relatively few 

 bacteria in proportion to the number 

 derived from other sources, it fre- 

 quently becomes desirable to use a 

 test that will reveal the amount of 

 visible sediment in the milk. For 

 this reason the committee has included 

 a description of the commonly used 



sediment test^*. In this way, valuable 

 information may be obtained and the 

 occasional approval of a dirty milk 

 prevented. As the sediment test be- 

 comes valueless if the milk has been 

 subjected to thorough straining or 

 clarification, or both, this test finds its 

 greatest use at milk receiving and 

 pasteurizing plants. 



Technique. 



After thorough stirring of the milk 

 in the can, or by inverting and shaking 

 a bottle, quart (or pint) samples of 

 milk shall be strained through cotton 

 disks placed over openings 1 inch in 

 diameter. This may be done satis- 

 factorily by means of any one of 

 several types of apparatus such as 

 the Schroeder, Lorenz Model,* and 

 Dairy mens Mfg. Co. It will hasten 

 the process of filtering in many cases, 

 if provision is made for warming the 

 milk. 



Method of recording results. 



In order tQ make comparisons be- 

 tween the work of different analysts, 

 standard gauges are given. A set of 

 these are photographed and given in 

 Figure L These gauges represent the 

 amount of dirt obtained by filtering 

 quart samples of milk to which have 

 been added 23^, 5, 7 and 10 milligrams 

 of the material which usually finds its 

 way into milk. The standards given 

 are intended for use where quart 



♦Creamery Package Mfg. Co. 



