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 
