ANIMAL FOOD III 



161. Butter. When milk remains quiet for some hours, 

 the fat rises to the surface in the form of cream. After 

 this is removed, milk is called skim milk. Cream is made 

 up of fine particles of fat, each surrounded by a thin 

 envelope of caseine. When cream is shaken until the 

 covering of the caseine is worn off, the fat collects in a 

 form called butter. The liquid part remaining is called 

 buttermilk, and does not differ much from milk, except 

 that the fat is mostly removed. Butter is the most valu- 

 able form of fat eaten. 



162. Value of milk. In sickness milk is almost the 

 only food which the stomach can digest at all. Only about 

 one twentieth of the solid part of milk fails to be digested. 

 When only milk is taken, there is but little residue upon 

 which the intestine contracts, and so waste matters pass 

 down the tube more slowly than when solid food is eaten. 

 Those who eat much milk find it profitable to eat heartily 

 of substances which, like oatmeal, leave a large undigested 

 residue to sweep out the waste matters of the intestine. 



163. Adulteration of milk. It is difficult to set a standard 

 for perfect milk, for no two cows give it of exactly the same composi- 

 tion. Milk which has a good quality of cream usually contains a good 

 quantity of albumin and sugar and so is said to be rich. Such milk is 

 yellow, in distinction from the bluish color of poor or skim milk. The 

 richness of milk may be measured by observing how thick a layer of 

 cream will rise in a deep glass tube full of milk. Another way is to 

 determine how much solid matter the milk contains by means of a 

 lactometer. This is a closed tube weighted so that it will float upright. 

 As more solid matter is dissolved in the milk, it becomes heavier and 

 will more easily sustain a body floating upon it. The richer the milk, 

 the less the bulb and tube will sink. This instrument is called a 

 lactometer. By means of it milk brought into large cities is tested by 

 government inspectors, and all milk which falls below a certain standard 

 is thrown away. The lactometer really records the specific gravity of 

 the milk. If it falls below 1.029, ** * s considered to be either watered 



