296 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



reduction time and the number of bacteria per c.c. to com- 

 pare as follows : 



1. Decolorization in 5% hours or over, less than 

 500,000 bacteria per c.c. 



2. Decolorization in from 2 to 5% hours, 500,000 

 to 4,000,000 bacteria per c.c. 



3. Decolorization in from 20 minutes to 2 hours, 

 4,000,000 to 20,000,000 bacteria per c.c. 



4. Decolorization in 20 minutes or less, over 20,000,- 

 000 bacteria per c.c. 



These figures do not apply to milk that has been 

 heated. 



The reduction time of market milk agrees in a general 

 way with the number of bacteria contained in the milk 

 and is a very good index to the "keeping qualities" or 

 stability of milk. The reductase test is not to be de- 

 pended upon to detect pathological milk. While mastitis 

 milk usually decolorizes in a shorter time than normal 

 milk, this does not occur in all cases. 



O. Jensen has combined the reductase test with the 

 fermentation test. 



FERMENTATION-REDUCTASE TEST 



This is a combination of the fermentation and re- 

 ductase tests which was first proposed by O. Jensen. 

 One-half c.c. of methylene blue solution is placed in a test 

 tube with 20 c.c. of milk, the tube is placed in an incubator 

 and kept under observation until decolorization occurs, 

 as in the reductase test. In addition, the test tube is 

 kept in the incubator until curdling occurs, and the type 

 of curd is then noted. Methylene blue in large quantity 

 inhibits the development of bacteria, especially the lactic 

 acid bacteria, but in the quantity used in this test the 

 effect is practically negligible. 



