=Cheese= is prepared by coagulating milk by “rennet,” the mucous membrane of the fourth stomach of the calf, salted and dried before using. By this means the casein is precipitated, carrying down with it the cream, and a large proportion of the salts of milk. The whey, containing the sugar, soluble albumin, and remaining salts, is separated by straining, while the mixed curd and fat are pressed in moulds. Cheese thus consists of casein, fat in varying proportions, water and salts, especially phosphate of lime. It is coloured with annatto, a vegetable colouring matter. When new, cheese is tough; when old, its oils tend to become rancid; the best age is from nine to twenty months. It is probable that cheese in small amount helps the digestion of other foods, though it is itself a highly concentrated and comparatively indigestible food. When toasted it is proverbially indigestible. There are many different kinds of cheese. The following classification gives the more important varieties:— (1) Cream cheese is the new curd only slightly pressed, and is more digestible than ordinary cheese. (2) Next to these are cheeses made with whole milk rich in cream, such as Stilton, Gorgonzola, Cheshire, and Cheddar. (3) Cheeses made of poor or partially skimmed milk, such as Shropshire, Single Gloucester, and Gruyère. (4) Cheeses made of skimmed milk, such as Suffolk, Parmesan, and Dutch. American cheeses may belong to any of these classes; they are generally pure, but occasionally are made from separated milk, margarine being added to take the place of cream. The sale of such cheeses, except under the name of “margarine cheese,” is now illegal. NON-NITROGENOUS ANIMAL FOODS.—These are all fats, and the most important are the various meat fats and butter. They possess a higher food value than carbohydrates in the proportion of 2¼ to 1. The composition of the various fats differs somewhat; they usually contain varying proportions of olein, palmitin, and stearin, which are compounds of glycerine with the radicle of a fatty acid (stearin = C₃H₅ (C_{18}H_{35}O₂)₃). Thus mutton suet consists of stearin, olein, and palmitin, with a preponderance of stearin. Beef suet contains less stearin and more olein than mutton suet. The more olein a fat contains the less solid it is. Olive oil is composed almost entirely of olein. Palmitin, which melts sooner than stearin, is the chief solid constituent of butter, while olein is its chief liquid constituent. Butter is specially distinguished by containing 7 to 8 per cent. of “volatile fatty acids,” such as butyric, caproic, etc., combined with glycerine. The presence and amount of these compounds is an important test for the freedom of butter from adulterating fats.