greatest. It is not unusual to find in the milk of a Jersey cow a content of 6 or 7 percent of fat.
Comparison of Cow's Milk with Other Varieties.—Human milk differs from milk chiefly in having a much lower content of casein and a higher content of milk sugar. Goat's milk has a higher content of casein than milk, somewhat higher content of fat, and slightly less sugar. Ewe's milk is very rich both in protein and fat. Mare's has a low casein and fat content and is exceptionally rich in sugar. Ass's milk has less casein and protein than milk but more sugar.
Cream.—When milk is allowed to stand for some hours in a cool place or when it is mechanically treated in a separator the fat particles, being of a less specific gravity, are separated, and when they reach a certain degree of consistence they form a product known as cream. The quantity of fat in cream varies according to the method of separation. On standing for a period of about twelve hours in a cool place the separated cream may be removed by skimming and should contain at least 18 percent of milk fat. Under the action of the separator, cream of a much greater content of fat is usually produced, often reaching as much as 30 percent or more. The separation of cream mechanically in a separator is preferable to the method of time separation by gravity alone. The cream secured by the separator is very much fresher, as it can be removed as soon as the milk is drawn and cooled. Its content of butter fat can also be regulated to the desired amount and, in the third place, a more complete separation is secured than by gravity. By the proper manipulation of the separator almost all of the fat in milk is readily removed. Cream should be kept under the same conditions as has been described for sanitary milk. When placed in sterilized containers, properly stoppered and kept cool, fresh cream will keep sweet as long as milk under similar circumstances.
In large dairy industries the separator is practically the only method now employed for securing cream while for farm use the gravity method of standing in a cool place for twelve or twenty-four hours is the commonly practiced method.
Cream is used on the table with fruit and cereal foods and especially in beverages such as tea and coffee. It is also prescribed by physicians for certain diseases and derangement of the digestive organs where the nitrogen content of milk produces irritation and fails of digestion. Cream is not a complete food in the sense that milk is inasmuch as the other constituents of milk are less in proportion as the percentage of fat is increased, yet cream contains at least a part of all the food elements in milk, as, for example, nitrogenous constituent, principally, casein, milk, sugar, and mineral matters.
It must be remembered in this case that the fat is the variable element and as as that is increased the proportion of other ingredients, necessarily, is diminished.
The most important use of cream is in the manufacture of butter.
