METHODS OF EXAMINING MILK 297 



A quickly reducing milk very frequently produces a 

 good curd (jelly-like) because in milk rich in bacteria 

 the lactic acid bacteria are often so numerous that they 

 inhibit the growth of the other species. But a milk may 

 reduce quickly and at the same time produce a bad curd 

 (gaseous or peptonized) ; such milk is extremely objec- 

 tionable. On the other hand, a slowly reducing milk may 

 produce a peptonized curd. This is because milk pro- 

 duced under cleanly conditions is exposed to a compara- 

 tively slight bacterial contamination and the udder cocci 

 consequently predominate. When such milk is kept at 

 a low temperature the peptonizing bacteria (udder cocci) 

 will develop more rapidly than the others and it will con- 

 tain few lactic acid bacteria. For these reasons, it has 

 been recommended by Barthel and O. Jensen that milk 

 with a reduction time of 5% hours or over should not 

 be condemned as bad on account of a peptonized curd. 



DIASTASE TEST 



Koning devised a method for the quantitative deter- 

 mination of diastase. The reagents used are a solution of 

 starch and a solution of iodine. The starch solution is 

 prepared by adding 1 gramme of soluble starch to 100 c.c. 

 of sterile distilled water, warming, and shaking the mix- 

 ture to bring about solution. The iodine solution is pre- 

 pared by dissolving 1 gramme of iodine and 2 grammes 

 of potassium iodide in 300 c.c. of distilled water. The test 

 is made as follows : 



Ten c.c. of milk is placed in each of five test tubes. 

 0.05 c.c. of the starch solution is added to the first tube, 0.1 

 c.c. to the second, 0.2 c.c. to the third, 0.25 c.c. to the 

 fourth and 0.3 c.c. to the fifth. The tubes are placed in 

 a water bath at 45 C. for 30 minutes, after which 1 c.c. 

 of the iodine solution is added to each tube. If all of the 



