90 DAIRY BACTERIOLOGY 



used, in which case the milk acquires a very disagreeable taste. 

 Moreover, the milk is appreciably affected by the milk enzyme 

 galactase (see under the ripening of cheese) in the course of a few 

 weeks, all of which goes to show that milk cannot be preserved for 

 any length of time without having recourse to strong heating 1 . 

 By adding substances containing catalase, such as liver extract 

 (Hepin), blood serum or yeast extract, the excess of hydrogen 

 peroxide may be removed immediately before the milk is used ; 

 this process was used on a large scale for the production of milk for 

 infant feeding (Perhydrase milk) on the estate of Prince Ludwig of 

 Bavaria. According to the author's researches, ozone has no bacteri- 

 cidal action on milk, and only gives it a highly disagreeable taste. 

 In this connection, mention may be made of the suggestion to 

 use the ultraviolet rays of the mercury arc lamp for sterilising milk. 

 As is known from Finsen's researches, these rays have a bacteri- 

 cidal action, and water has been sterilised on a large scale in this way. 

 Milk, however, is somewhat impervious to the rays and, moreover, 

 it generally contains highly resistant spores ; it is therefore 

 doubtful whether the method will ever come to have any practical 

 significance, notwithstanding the number of appliances which have 

 already been devised for carrying it out. Powerful alternating 

 currents are said to have been applied with greater success. 



TREATMENT OF MILK FOR TOWN SUPPLIES 



As the general methods usually available for producing good 

 milk have already been discussed, the subject of the proper treat- 

 ment of milk which is to be retailed in towns may be dealt with quite 

 briefly. The difficulties to be faced are often considerable, for as 

 the milk has often to be sent long distances by railway, it may not 

 reach the consumer until it is six to thirty hours old, and even 

 then it may have to stand for a long time under unfavourable 

 conditions before it can be used up. Only milk which has been 

 cleanly handled from the outset can be expected to keep good 

 under these conditions. On arrival at the large dairies, the milk 

 is first graded, smelt and tasted, and frequently sampled for 

 further examination. After weighing or measuring, the milk is 

 freed from particles of dirt by filtering or centrifuging. This 

 treatment, at a stage when the bacteria have long since been 

 distributed throughout the milk, can only be justified on sesthetic 

 grounds ; it can have no influence on the keeping power of the 

 milk. Some of the bacteria will naturally be removed, but, on the 

 other hand, large clumps of bacteria are broken up with the result 



1 As hydrogen peroxide itself has a solvent action on proteins, it will 

 rather promote the action of the proteolytic enzymes than inhibit it. 



