32 THE MILK QUESTION 



sugar into lactic acid through the action of different bacte- 

 ria. This acidity increases until finally enough acid is pro- 

 duced to cause the souring or curdling ordinarily observed. 



Under the microscope milk contains fat globules as well 

 as cells, and bacteria, and frequently foreign particles of 

 great variety of form and size. 



The following table is compiled from a large number of 

 analyses of milk and milk products which have been made 

 by chemists of the agricultural experiment stations and 

 other investigators. The figures show the average com- 

 position of these materials. The table also includes, for 

 purposes of comparison, the average composition of a num- 

 ber of other common food materials: 



AVERAGE COMPOSITION OF MILK PRODUCTS AND OTHER 

 FOOD MATERIALS 



