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 3 per cent, solutions and must therefore be 



