298 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
starch has been digested the mixture in the tube assumes 
a citron-yellow color; if any starch remains a blue color 
will appear. According to Koning, normal milk will 
digest the starch in the first two or the first three tubes; 
a higher diastatic power indicates mastitis, while a lower 
indicates old milk. Others report that the diastatic power 
of milk from cows affected with mastitis is very variable 
and that the diastase test cannot therefore be depended 
upon to discover mastitis milk. The diastatic power is 
also increased in the colostral period and near the end of 
lactation. One observer affirms that the diastase in milk 
is decreased when the ration is rich in carbohydrates. 
TESTS FOR HEATED MILK 
Two tests are used to determine whether or not milk 
has been heated to 80° C. (176° F.) or above. They are 
as follows: 
Storch’s Test.—5 c.c. of milk or cream is placed in a 
test tube, 1 drop of 0.2 per cent. solution of hydrogen 
peroxide containing 0.1 per cent. of sulphuric acid, and 
2 drops of a 2 per cent. solution of paraphenyldiamin are 
added, and the mixture is shaken. If the mixture as- 
sumes an indigo blue or violet color immediately, it has 
not been heated at all or not higher than 78° C. (172.5° 
F.) ; if it becomes a light bluish-gray within a half min- 
ute, it has been heated to between 79 and 80° C. (174.2° 
to 176° F.) ; if it remains white, it has been heated to at 
least 80° C. (176° F.). Raw whey gives a violet or red- 
dish-brown color. 
Arnold’s Guaiac Test.—A small quantity of milk is 
placed in a test tube and a little tincture of guaiac is run 
down the side of the tube drop by drop so that it will 
not mix with the milk but form a layer on top of the milk. 
If the milk is raw or has not been heated to 80° C. 
