In countries where fresh milk cannot be had, milk is condensed to preserve it for use. It is evaporated in vacuo until it becomes thick and paste-like. Two kinds of condensed milk are to be had in the market: one unsweetened, the other containing cane-sugar. In the former the proportion of water is reduced from 88 to 60 per cent. The latter contains from 40 to 75 per cent, of sugar. Condensed milk is often used as an infant's food. Some children grow fat upon it, but rarely thrive long. They are prone to rachitis. Their flesh is generally soft, and they do not resist disease well.

Cream contains most of the fat of milk. It is obtained either by permitting milk to stand, when the fat will rise to the top and can be skimmed off, or it may be obtained more rapidly and perfectly by means of the centrifugal cream separators now so generally used by dairymen. The proportion of fat in cream varies greatly. Ordinarily it is from 15 to 20 per cent, of the whole. Cream separators will produce a cream containing 65 per cent. fat. It is quite as essential that a legal standard should be fixed for cream as for milk. Cream contains about the same percentage of protein and sugar as milk. The fat in it displaces only some of the water that milk contains.

Cream is agreeable to most persons, and is one of the most easily digested fats. Although not quite so digestible as cod-liver oil, it is an excellent substitute for the latter, because it is more willingly taken in sufficient quantities. A pint of cream will furnish 125 more calories (1425 calories) than four quarts of milk. It is a heat producer or energy producer, and should be supplemented by porteins to make a complete diet.

Ice-cream, when made simply, is wholesome and agreeable. It may be fed to many invalids with benefit. It is cream flavored with vanilla, sweetened with sugar, and frozen. Icecream that contains rich flavoring extracts or much fruit is less easily digested.

Skimmed milk is the residue left when cream is removed from milk. It is milk poor in fat. Its composition varies inversely as that of the cream that has been removed from it.

It is adapted for use when the fat of milk cannot be well digested.

Butter is produced from cream by churning. In this process the albuminous envelops of the fat globules of the cream are broken and the fat particles are permitted to commingle and to form a solid mass. The fluid residue contains most of the sugar and protein of the cream. The flavor of butter is derived from the growth of organisms in it while it is ripening. In many creameries pure cultures of certain micro-organisms are now used to ripen butter and thus insure a uniform flavor to their product, or to adapt the flavor to the preference of certain markets. Butter prepared from fresh cream has not what is known as the butter flavor. It is comparatively insipid. Salt is mixed with butter to preserve it and to flavor it. When butter is not salted, it spoils quickly. When it spoils it becomes rancid, bitter, and unwholesome. These changes take place readily if it is kept in too warm a place.

Two one-inch cubes of butter weigh approximately an ounce and furnish 284 calories and 0.38 grams of protein.

Butter is often adulterated by coloring matters and by admixtures of other fats. Margarin is prepared from ox fat, and is quite as digestible and wholesome as butter. When mixed with it, an agreeable fat results that is much cheaper than butter. It is known as butterin. If it is well made, it is not harmful. Butter that has become partly rancid may be washed repeatedly with hot water and again 'worked'; it will taste nearly as well and be as cheap as butterin, but it is not equally wholesome.

Most persons eat an ounce of butter or more daily. As a rule, it is very easily digested. Although it is less digestible when cooked than when used cold.

Butter contains from 12 to 5 per cent, of water, 82 per cent, of fat, and about 2 per cent, of other organic matter. Margarin contains 9.3 per cent, of water, 1.3 per cent, of protein, 82.7 per cent, of fat, and 6.7 per cent, of ash (Atwater).

Buttermilk, or the residue after butter is made from milk, contains albumin, salts, sugar, and water. Much of the sugar is converted into lactic acid and gives to buttermilk its sour taste. It is relished by many persons and particularly well digested by those who cannot eat fats.

In Turkey, Bulgaria, Servia and the neighboring countries sour milk has been used as a beverage very generally and is preferred to sweet milk. The bacterium caucasicus or Bulgarian bacillus is the most active of the lactic acid ferments. It has been observed that it will, when introduced into the intestinal tract in large numbers, check the growth and thereby greatly lessen the number of other organisms in it. Buttermilk is therefore especially useful to lessen fermentation in the intestines.

Of late years it has been largely used because Metchnikoff has praised it as an elixir of long life. He believes that arteriosclerosis and the lesions caused by it are due to bacterial fermentation of food products in the intestines and he urges the drinking of buttermilk or the taking of lactic acid ferments to prevent this.

However, there is not sufficient positive experimental evidence to show that lasting effects of this kind can be produced by the lactic acid ferments or by the Bulgarian bacillus especially. Moreover there is some evidence to prove that certain micro-organisms are needed in the intestines to complete digestion, and therefore to maintain good health.

Cheese is a product of milk and is composed of its casein and fat. The casein is precipitated either by permitting the milk to sour or by adding acids or rennet to it. Cheeses vary in composition according as they are made of milk to which cream has been added, of whole milk, or of skimmed milk. In this way the relative quantity of fat that they contain is made to vary. They are modified in consistence according as the curd is pressed into hard cakes or left as a soft mass and shaped by the hand of the maker or by light pressure. The peculiar flavor of cheese is due to special micro-organisms that, by their growth during the period of 'ripening,' develop in it chemical bodies of peculiar flavor.

The soft cheeses, such as cream cheese, Brie, Camembert, Neufchatel, and Stilton, must be eaten fresh, as they will not keep long.

The hard cheeses, such as American dairy, Parmesan, and Edam, will keep for a long time.

With few exceptions cheese is made from cow's milk. Parmesan is made from goat's milk partly skimmed, and Roquefort from the milk of the ewe.

The following table, taken from Hutchison, shows the composition of many of the common cheeses:1

In general it may be said that cheese contains approximately one-third water, one-third nitrogenous matter, and one-third fat. It would seem to be a most concentrated and cheap nitrogenous food. A pound of lean meat contains over 70 per cent, of water. Mattieu Williams says that a cheese of twenty pounds contains as much nutriment as a whole sheep weighing sixty pounds. A pound of cheese will produce at least 2000 calories. This is more than three times as much as a pound of lean beef will yield.

Although, from its composition, cheese appears to be so perfect a nitrogenous food, it illustrates well the fact that the value of articles of food cannot be estimated by their composition alone. Cheese is not easily digested. The fat that it contains surrounds the particles of casein of which it is chiefly composed and prevents the gastric juice from coming readily

1For a full description of all of the many kinds of cheese and their composition, see "Varieties of Cheese," Bulletin 146, U. S. Department Agriculture, Bureau of Animal Industry, 1911 in contact with them. Cheese is most easily digested when it is eaten in a state of fine subdivision or in solution, as recommended by Williams. It can be readily dissolved by a small amount of potassium bicarbonate. A savory and nutritious dish can be prepared by adding milk and eggs to this dissolved cheese.

Certain cheeses contain fatty acids that are developed in the process of ripening. They are frequently irritating to the stomach.

Cheese, like other milk products, may contain tyrotoxicon and cause even fatal poisoning. This ptomain is the product of a specific micro-organism which sometimes infects milk and its products without materially modifying their appearance or taste.