204 



season. This acid is also produced by the direct action 

 of caseine upon the fats of the butter themselves, chang- 

 ing the harder fats into the more oily ones, and thus 

 causing the butter to be soft and of inferior quality. The 

 oxygen of the atmosphere has also the same result. 

 These facts show how necessary it is to preserve the ut- 

 most freedom from any remains of stale milk or cream 

 upon the utensils, to preserve the milk from excess 

 of heat and from currents of air, as well as from the en- 

 trance of any injurious matter into the cow. 



Milk is thus a serous or albuminous fluid, in which 

 a varying quantity of sugar, caseine, and mineral salts 

 are dissolved and in which a varying quantity of fat or 

 oil in the form of very minute globules are mechanically 

 suspended in the manner of an emulsion (figure 25, d). 

 .*,. The sugar, caseine and fat are each of 



fi'^/ol'^** Tj them the basis of a profitable manufacture; 

 •♦•/^*«* the sugar is separated and used in various 



ways as milk sugar ; the caseine and fat 



-!{5^^ are made into cheese, and the fat is gath- 



^M^ ^ ered and made into butter. When left at 



' " rest for a time the fatty globules rise to 



Fig. 25. ^^Q surface, together with some of ad- 



herent milk, by virtue of their lighter specific grav- 

 ity, and controlled as to time by various conditions 

 of the milk and the temperature, they form what 

 we know as cream (figure 25, e). These fat glob- 

 ules were supposed to consist of a pellicle or film of 

 caseine enclosing a granule of fat, as it is set free 

 by the breaking down of the vesicles or acini of the 

 glandular lobules of the udder. This supposition 

 was held to be unreasonable and erroneous by the au- 

 thor, who opposed this view of it as supported by 

 Professor Arnold, the eminent authority upon the 

 science and practice of dairying, at a meeting of the 

 American Dairymen's Association in 1872. Since then 



