METHODS OF EXAMINING MILK 291 
correct result. Increases of 0.8 to 1 c.c. have been ob- 
served after agitation. 
6. After the reading is taken, the volumeter is dis- 
connected from the bottle, the stopper inserted in the top, 
and the water forced from the outer to the middle tube 
by pressure on the stopper until the two columns of water 
are level with each other. The volumeter is then ready to 
be used again. The bottle is emptied and cleaned and 
sterilized for the next test. 
Milk from one or several cows in normal condition, 
tested within three hours after being drawn from the 
udder, will not show over 3 c.c. of oxygen at the end of 
the second hour. If the milk is not tested within three 
hours, the oxygen reading will be in excess of this figure, 
because the catalase in the milk at the time it was secreted 
will have been added to by that produced by the bacteria 
in the milk. According to Faitelowitz and others, if 2 per 
cent. of chloroform is added to the milk the power or ac- 
tivity of the catalase existing at the time is not affected, 
while the secretion of catalase by bacteria is prevented. 
Certain physiological conditions cause an increase in 
the catalase. Colostrum, milk for 4 to 5 days up to 3 
weeks after calving, and milk from “strippers” yielding 
only a quart or less a day give a higher oxygen reading 
- than is normal for milk at other stages of lactation. The 
oxygen reading is also increased after sudden or pro- 
nounced changes in feed, following incomplete milking 
and stasis of milk, and sometimes in oestrum when the 
cow is nervous and excitable. 
In disease of the udder, when individual milk is tested, 
the oxygen reading is above normal before any clinical 
symptoms are apparent and before there are any visible 
changes in the appearance of the milk. The reading 
