METHODS OF EXAMINING MILK 287 
absorbed from the diseased area and eliminated, in part 
at least, through the udder. While a negative reaction 
may not always indicate the entire absence of disease, the 
presence of any diseased condition which affects the 
udder directly or indirectly is indicated by a positive re- 
action, excluding, of course, cows which are “fresh,” near 
the end of lactation, in heat, or which have recently 
aborted. 
The alcohol test is a more delicate test for bacterial 
decomposition and for the presence of inflammatory and 
other pathological products than the boiling test and will 
give a positive reaction when the boiling test is negative. 
CATALASE TEST 
The amount of catalase in milk is measured by the 
amount of oxygen which is separated when a measured 
quantity of hydrogen peroxide is added to a certain quan- 
tity of milk. Different forms of apparatus are used for 
collecting and measuring the oxygen, the one most com- 
monly used being the Gerber-Lobeck apparatus. 
The quantity of oxygen separated will depend not 
only on the amount of catalase in the milk, but also upon 
the amount of hydrogen peroxide added. The quantity 
of oxygen separated increases with the amount of hydro- 
gen peroxide added up to a certain point, but if hy- 
drogen peroxide is present in excess of this amount it 
will exert a depressing effect upon the ferment. For 
this reason it is necessary to standardize the hydrogen 
peroxide solution used, and since the solution is unstable 
it must be standardized from time to time. 
A 1 per cent. solution of hydrogen peroxide is used 
in the test. The ordinary preparations of hydrogen per- 
oxide are 8 per cent. solutions and must therefore be 
