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EXPERIMENTAL DAIRY BACTERIOLOGY 



Exercise. Each student will make a quantitative examination of 

 three samples of milk : (1) fresh milk; (2) ordinary market milk ; 

 (3) milk having a high acidity (0.3-0.4 per cent). 



The dilutions to be used in the examination of the different milks 

 should be indicated by the instructor. 



Arrangement of data. The complete data should be ar- 

 ranged in tabular form as far as possible, so as to facilitate 

 the examination of the results. The following may serve as 

 an example of arrangement : 



Method for comparative results. When it is desirable to 

 determine merely the relative number of bacteria in a num- 

 ber of samples, as, for example, in sweet and ripened cream, 

 a different method may be used, which is sufficiently accurate 

 for the purpose. 



A standard-sized loop is made of No. 27 platinum wire by 

 making the loop around an eight-penny common nail (10| 

 wire gauge). The loop should be made as illustrated (Fig. 7). If 

 it is always used in the same way, i.e. immersed to the same 

 depth in the liquid, removed quickly, and the lumen of the 

 loop kept parallel to the surface of the liquid, a double con- 

 vex drop of liquid will be removed, which will contain an ap- 

 proximately uniform quantity of milk (0.008 to 0.012 grams). 

 High dilutions can thus be obtained by the use of small water 

 blanks (5 cc.), and the use of many pipettes avoided. 



