166 Milk and Its Products 



globules ; second, the amount of solids not fat in 

 the milk ; third, the character of the solids not 

 fat. The larger the fat globules the more readily 

 they separate from the milk, since the larger the 

 sphere the less the ratio between the surface and 

 the mass, so that a large fat globule meets with pro- 

 portionately less resistance because of the viscosity 

 of the milk than a small one. The size of the fat 

 globules is to a great extent a characteristic of the 

 breed and individuality of the animal, but cows 

 newly calved secrete larger fat globules than those 

 in advanced periods of lactation ; consequently we 

 find that the milk from new milch cows is more 

 readily creamed than from those long in milk. 

 The amount of solids not fat affects creaming by 

 the gravity process because of the difference it effects 

 in the specific gravity of the fat and milk serum. 

 The solids not fat are all heavier than water, and 

 in the milk are in a state of solution or semi -solu- 

 tion ; hence, an increase in the amount of solids not 

 fat increases the specific gravity of the milk serum 

 in which they are dissolved, and makes the differ- 

 ence between the specific gravity of the fat and 

 milk serum greater and the separation of the fat 

 easier. The proportion of solids not fat is in- 

 fluenced by the period of lactation and, to a con- 

 siderable extent, by the character of the food. Cows 

 far advanced in lactation often give milk extremely 

 rich in solids not fat. Cows fed on dry food give 

 milk containing less water than those fed on watery 

 or succulent foods. In so far as these conditions 



