METHODS OF EXAMINING MILK 301 
below normal the color remains yellow or orange. When 
the color becomes yellowish-brown the condition of the 
milk must be regarded as doubtful. The presence of a 
large amount of fat is likely to interfere with the reaction 
and it is therefore best to remove the fat from the milk 
before applying the test. Milk sugar is decreased in 
quantity and is sometimes entirely absent in inflamma- 
tion of the udder. It is also reduced in quantity during 
the colostral period and toward the end of lactation; 
exercise sometimes decreases it. It is present in greatest 
amount in the middle of a milking and lowest at the 
beginning and end. Fresh market milk will always give 
a normal reaction to this test. 
EXAMINATION FOR COLORING MATTERS 
When the yellow color of milk is natural it is largely 
confined to the cream, and if opportunity is given for 
the cream to rise the milk beneath it has a bluish tinge. 
But when the yellow color is artificial not only the cream 
but the milk beneath it is of the same color. Artificial 
coloring matters are sometimes added to milk to give it 
a rich color when it has been adulterated with water. 
Annatto, also called arnatto and annotto; analin orange, 
an azo-dye, and caramel are the substances most fre- 
quently used. Leach recommends the following pro- 
cedure for the detection of artificial coloring: 
Place 150 c.c. of milk in a casserole, add a little acetic 
acid and heat until curdling occurs. Gather the curd 
together with a glass rod and pour off the whey, or sepa- 
rate by filtration. Macerate the curd with ether in a 
stoppered bottle for several hours. Evaporate the ether 
extract on a water bath, add sufficient sodium hydroxide 
to the residue to make it alkaline and pour the mixture 
