36 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



milk of normal cows are likely to balance one another 

 when the milk of several cows is mixed together; con- 

 sequently different samples of market milk show less 

 variation in the number of leucocytes than individual 

 milk. On the other hand, when the milk from one cow 

 affected with mastitis is mixed with the milk of other 

 cows in the herd which are in normal condition, the cell 

 content of the mixed milk is not likely to be very much 

 increased unless the herd is a very small one or the milk 

 from the diseased cow contains an enormous number of 

 cells. 



Several methods have been devised for detecting an 

 excessive number of cells in milk (see pages 281 to 284) . 

 When used to examine the milk of individual cows, 

 these methods are of great assistance in discovering cases 

 of mastitis before clinical symptoms or visible milk 

 changes appear, but when applied to samples of mixed 

 market milk they cannot be depended upon entirely for 

 the purpose of detecting mastitis in the herds supplying 

 the milk. 



BIOLOGICAL PROPERTIES OF MILK 



Ferments or Enzymes. Milk contains a number of 

 ferments or enzymes. Some of them resemble the di- 

 gestive ferments in their action. This class includes a 

 proteolytic ferment called galactase, and diastase, an 

 amylolytic ferment. These ferments are believed to 

 assist in the digestion of milk. A tripsin-like ferment 

 and fat-splitting ferments or lipases have been reported, 

 but their existence is questioned. There are also oxidiz- 

 ing ferments : the oxydases and peroxydase, and reduc- 

 ing ferments: catalase and reductase. The diastase, 



