METHODS OF EXAMINING MILK 267 



an unwarranted impression of accuracy. For example, 

 when the numbers are in millions no figures smaller than 

 the millions have any significance in the routine analysis 

 of milk. In making the report raise the number to the 

 next highest round number, but never lower it. 



" In no case shall the count of a single plate be re- 

 garded as sufficient for the purpose of grading milk. If 

 a single sample of milk only is to be tested there should 

 be at least three plates counted before a report is made." 



MICROSCOPIC METHOD 



The apparatus required for this method consists of 

 a microscope, a supply of ordinary glass slides, and a 

 straight capillary pipette marked to deliver 1/100 c.c., 

 with the graduation mark 1% to 2% inches from the tip. 

 The calibration should be tested by weighing on chemical 

 balances the quantity of milk delivered when the pipette 

 is filled to the mark. One pipette may be used for a num- 

 ber of samples of milk provided it is kept clean. This 

 may be done by rinsing the interior with clean water 

 after each sample and wiping the exterior with a clean 

 towel. 



Preparation of Smears. " One one-hundredth c.c. 

 of milk or cream is deposited upon a clean glass slide by 

 means of the pipette above described. By the use of a 

 clean stiff needle this drop of milk is spread over an 

 area of one square centimetre. This may be most con- 

 veniently done by placing the slide upon any glass or 

 paper ruled into areas one centimetre square. These 

 marks showing through the glass serve as guides. After 

 uniform spreading the preparation is dried in a warm 

 place upon a level surface. In order to prevent notice- 

 able growth this drying must be accomplished within 



