3. _The proteids_ form a part of all the tissues, and for this reason are stored in larger quantities than any of the other food substances. The large amount of proteid found in the blood may also be looked upon as storage material. The proteids in the various tissues are spoken of as _tissue proteids_, and those in the blood as _circulating proteids_. The proteids of the tissues serve the double purpose of forming a working part of the cell protoplasm, and of supplying reserve food material. That they are available for supplying energy, and are properly regarded as _storage material_, is shown by the rapid loss of proteid in starving animals. When the proteids are eaten in excess of the body’s need for rebuilding the tissues, they are supposed to be broken up in such a manner as to form glycogen and fat, which may then be stored in ways already described. *General Facts Relating to Storage.*—The form into which the food is converted for storage in the body is that of _solids_—the form that takes up the least amount of space. These solids are of such a nature that they can be changed back into their former condition and, by dissolving, reënter the blood. Only energy-yielding foods are stored. Water and salts, though they may be absorbed in excess of the needs of the body, are not converted into other substances and stored away. Oxygen, as already stated (page 108), is not stored. The interval of storage may be long or short, depending upon the needs of the body. In the consumption of stored material the glycogen is used first, then as a rule the fat, and last of all the proteids. *Storage in the Food Canal.*—Not until three or four hours have elapsed are all the nutrients, eaten at a single meal, digested and passed into the body proper. The undigested food is held in reserve, awaiting digestion, and is only gradually absorbed as this process takes place. It may properly, on this account, be regarded as _stored material_. That such storage is of advantage is shown by the observed fact that substances which digest quickly (sugar, dextrin, "predigested foods," etc.) do not supply the needs of the body so well as do substances which, like starch and proteids, digest slowly. Even substances digesting quite slowly (greasy foods and pastry), since they can be stored longer in the food canal, may be of real advantage where, from hard work or exposure, the body requires a large supply of energy for some time. These "stay by" the laborer, giving him strength after the more easily digested foods have been used up. Storage by the food canal is limited chiefly to the stomach.