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 54% 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. 
8. 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. 
