290 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



quantity of milk obtained at a milking, or from the total 

 quantity obtained from each quarter, if it is desired to test 

 each quarter separately; but when this is not convenient, 

 50 to 100 c.c. of milk may be drawn from each quarter 

 directly into a sterile sample bottle, after discarding the 

 first three expressions from each teat. In either case, the 

 sample should be thoroughly mixed before the amount 

 required for the test is drawn off. 



3. The volumeter, properly filled with water free 

 from air bubbles, is closed at the top with a rubber stop- 

 per and is then inserted into the perforated stopper of the 

 bottle. The perforated stopper must be forced down 

 sufficiently to close the small hole in the neck of the bot- 

 tle. The fluids are mixed by gently whirling the bottle, 

 care being taken not to wet the stopper. 



4. The apparatus is set aside at a temperature of 20 

 to 25 C.; in winter a water bath is necessary, but only 

 the bottle should be placed in the water. The rubber 

 stopper in the upper end of the volumeter should be re- 

 moved in order to avoid any counter-pressure against 

 the water being forced from the middle chamber of the 

 volumeter to the outer by the pressure of the oxygen 

 separated from the hydrogen peroxide in the bottle. The 

 bottle is then permitted to stand for two hours, when the 

 amount of oxygen is read off. 



5. The amount of oxygen separated is indicated by 

 the extent to which the water in the inner tube of the 

 volumeter has been forced downward. Before taking 

 the reading as final, the bottle should be gently whirled 

 until the volume of oxygen remains constant. Without 

 such agitation, some of the gas may remain in the bottle, 

 adherent to the fluid, and the reading will not give the 



