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: 



Storclis 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. 



