160 



DAIRY BACTERIOLOGY 



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for this reason, milk drawn from cows with diseased udders or from 

 cows which are approaching the end of the lactation period, or 

 colostrum, will liberate large amounts of oxygen from hydrogen 

 peroxide. As the fat globules carry with them large numbers of 

 leucocytes, unpasxeurised cream, obtained either 

 by spontaneous separation or by the use of the 

 separator, will be richer in leucocytes than the 

 corresponding skim milk. Many ingenious and 

 sometimes complicated forms of apparatus have 

 been devised for the carrying out of the test. 

 In the author's laboratory Lind's apparatus is 

 used ; this consists simply of a graduated tube 

 of 20 c.c. capacity, into which 15 c.c. of milk are 

 introduced ; sufficient hydrogen peroxide (1 to 3 

 per cent.) is added to fill the tube, the rubber 

 stopper carrying the bent tube is inserted, and the 

 apparatus is inverted as shown in the illustration. 

 The maximum amount of oxygen is obtained at 

 20 to 25 C., so that no water bath or thermostat 

 is necessary. The number of cubic centimetres 

 of oxygen evolved in six hours is taken as the 

 catalase number. Fresh milk from healthy cows 

 will not yield more than 2-5 c.c. In mixed milk 

 the blood corpuscles will be too sparsely distributed to produce 

 any recognisable effect. The milk must be perfectly fresh 

 when tested, as many bacteria decompose hydrogen peroxide. 

 The common sarcinae and micrococci (see p. 38), e.g., Micrococcus 

 candicans, and most of the putrefactive bacteria are particularly 

 active in this respect, while the true lactic acid bacteria and the 

 butyric acid bacteria l do not produce catalase. Milk which has 

 stood for any length of time at a low temperature, or old pas- 

 teurised milk, will accordingly show high catalase values. Hesse 2 

 has proposed to apply the catalase test to butter as follows : 

 100 grams of butter are warmed to 45 C. and shaken with 40 c.c. 

 of water at this temperature ; the aqueous liquid is separated and 

 tested in the same way as milk. It is obvious that butter which 

 has been made from pasteurised cream ripened with a pure starter 

 of lactic acid bacteria will show a low catalase figure ; if the 

 butter has been washed with bad water it may show a high catalase 

 figure, for Bacterium fluorescens liquefaciens is particularly active 

 in decomposing hydrogen peroxide. 



1 Orla Jensen, " Det. kgl. danske Videnskabers Selskabs Oversigter " 

 (Danish Academy of Sciences), 1906, No. 5, p. 306. 



2 " Molkereizeitung," Hildesheim, 1912, No. 6. 



FIG. 65. Catalase 

 Test Apparatus. 



