A. Examine the ends of a shin-bone sawed in two. Where is the bone the hardest? Where is it spongy? Where soft? The soft substance is marrow. Try to bend or break the bone. Observe the tough fibrous covering on the ends of it.

B. Put one piece of the bone in diluted hydrochloric acid (six parts of water to one part of acid); after a few days compare it with the other piece. Has the acid changed the shape of the bone? its size? How has it affected it? See if you can tie it in a knot. What makes bone hard? What, then, has the acid taken out of the bone?

C. Tie a wire around the other piece of bone, and lay it for half an hour in a hot coal-fire. Remove it by means of the wire. How has it changed? Does it break easily? What part of the bone has been burned?

Structure And Composition Of Bone

Bone is the hardest of animal tissues, yet it is one-half water; the other half consists of about two-thirds mineral, and one-third animal matter, the mineral being largely calcium phosphate, commonly called phosphate of lime; the animal matter chiefly fat and collagen.1 In the centre of hollow bone is a mass of fatty stuff, the marrow. Surrounding, and, in some cases, forming the end of the bone is the flexible, slippery substance called cartilage, or gristle; and, connecting bones at the joints, are bands or ligaments of cartilage. Cartilage may be considered soft bone, since it differs from bone mainly in having less mineral matter. The bones of children and young animals are soft because they are cartilaginous; the older the individual grows, the harder the bones become. The two kinds of material in bone may be separated by soaking in acid, which dissolves the inorganic substance; or by burning, which destroys the organic.

1 Often called ossein in bones.

How Cooking Affects Bones

By long cooking in water the insoluble collagen and similar substances of connective tissue, tendon, cartilage, and bone are changed to gelatin, soluble in hot water.1

But will hot water best draw out the meat juice? How may we contrive to extract all possible food value from both meat and bone? And how may we also give to soup that rich flavor produced only by heating meat to above 212° F. ? All these points must be considered if we mean to make the best possible soup out of our materials.

The Soup-Kettle Or Stock-Pot

Have for stock-making a deep kettle with a tight-fitting cover; the tighter the cover the smaller is the amount of water lost by evaporation. In an ordinary kettle, stock may, during cooking, lessen by one-half; in a soup-digester with a steam-tight, valved cover, evaporation is so slight that one pint of water instead of one quart may be allowed to one pound of meat and bone.

Fresh material may be added to that already in the stock-pot, provided that once a week the contents are removed and the pot cleaned. Fresh material must be combined with "left-overs" for a satisfactory stock, cooked meat alone yielding too little soluble material. Fresh herbs and, unless a varied stock of cooked vegetables is on hand, a few fresh vegetables are required for flavoring.

1 In changing to gelatin, collagen takes up water, something as starch does in changing to starch-paste.

Materials For Soup-Stock

Put raw-meat trimmings cut off by the butcher, flank ends of steak, etc., into one jar, bits of cooked meat and bone, except mutton fat, which is rank in flavor, into another jar. Keep the water in which meat has been cooked. Keep separately, because it sours in about two days - quicker than meat-liquor spoils - the cooking water from rice and vegetables. Use sparingly water from strong-flavored vegetables, such as onion and turnip, and do not use cabbage or potato water at all.

Celery and asparagus water may be used either for soup-stocks or for cream-of-vegetable soups. (Chap. VIII, sect. 3.) Keep by themselves, and separate from one another, if possible, remnants of vegetables, rice, macaroni, etc.

How To Choose Soup Meat

What sort of meat shall we choose for soup-making, - tender or tough, with bone or without ? What advantage has the meat from young creatures over that from old ? Soup meat should include some fat, because the cake formed by it when cold, if kept unbroken, helps to preserve the stock.

Compare a cut from the loin of beef with one from the leg (shin). Compare a shin of beef with a knuckle of veal (the joint of a calf's hind leg). Which will yield the most juice? the most gelatin? the highest flavor? Which of these cuts would you expect to find the cheapest? Why?