Along with its dry matter, its protein, its carbohydrates, and its fats, milk and its products possess another most important property. This property is hard to describe, for its elements and its powers are not yet fully understood. We do, however, know certainly this much: milk and the foods made from it have power to promote health and favor growth in a more marked degree than any other foods. It is generally agreed that this is due to the health-promoting and health-preserving substances which are called vitamines. Men of science are working with much care to try to add to our knowledge of these vitamines, which have so marvelous an influence on the health of all animals. Unless food, no matter how good otherwise, contains these vitamines, it does not nourish the body nor preserve bodily health as it should. A complete lack of vitamines in our food would cause death. Since, then, milk and its products--butter, cheese, curds--are rich in vitamines, these health-giving and health-preserving foods should form a regular part of each person's diet. [Illustration: FIG. 270. AIRING THE CANS] =Cream.= Cream is simply a mixture of butter-fat and milk. The butter-fat floats in the milk in little globe-shaped bodies, or globules. Since these globules are lighter than milk, they rise to the surface. Skimming the milk is a mere gathering together of these butter-fat globules. As most of the butter-fat is contained in the cream, pains should be taken to get all the cream from the milk at skimming time. After the cream has been collected, it must be allowed to "ripen" or to "sour" in order that it may be more easily churned. Churning is only a second step to collect in a compact shape the fat globules. It often happens that at churning-time the cream is too warm for successful separation of the globules. Whenever this is the case the cream must be cooled. [Illustration: FIG. 271. A HAND SEPARATOR] =The Churn.= Revolving churns without inside fixtures are best. Hence, in buying, select a barrel or a square box churn. This kind of churn "brings the butter" by the falling of the cream from side to side as the churn is revolved. Never fill the churn more than one-third or one-half full of cream. A small churn is always to be avoided. =Churning.= The proper temperature for churning ranges from 58 deg. to 62 deg. Fahrenheit. Test the cream when it is put into the churn. If it be too cold, add warm water until the proper temperature is reached; if too warm, add cold water or ice until the temperature is brought down to 62 deg.. Do not churn too long, for this spoils butter. As soon as the granules of butter are somewhat smaller than grains of wheat, stop the churn. Then draw off the buttermilk and at a temperature as low as 50 deg. wash the butter in the churn. This washing with cold water so hardens the granules that they do not mass too solidly and thus destroy the grain.