METHODS OF EXAMINING MILK 291 



correct result. Increases of 0.3 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 



