Although milk is made up mainly of water it contains nearly all the food substances needed by the body. That is why it is a valuable drink for children and is used in so many different ways in our diet. Milk looks white because it contains a protein (body-building substance) called casein. Through a microscope floating globules (small drops) of fat can be seen in milk. The layer of cream which floats on the top of milk is made up of fat globules, as well as casein and fat, which can both be seen. Milk also contains a type of sugar called lactose dissolved in it. Minerals particularly calcium and phosphorus (which are important in forming bones and teeth) and most of the vitamins essential for life and health are also contained in milk and milk is produce by all mammals to feed their young for the first part of their lives, all young mammals from whales to babies because milk is a useful food for adults as well as for babies and children.