*Tissue Enzymes.*—The important part played by enzymes in the digestion of the food has suggested other uses for them in the body. It has been recently shown that many of the chemical changes in the tissues are in all probability due to the presence of enzymes. An illustration of what a tissue enzyme may do is seen in the changes which fat undergoes. In order for the body to use up its reserve fat, it must be transferred from the connective tissue cells, where it is stored, to the cells of the active tissues where it is to be used. This requires that it be reduced to the form of a solution and that it reënter the blood. In other words, it must be _redigested_. For bringing about these changes a substance identical in function with the steapsin of the pancreatic juice has been shown to exist in several of the tissues. Although this subject is still under investigation, it may be stated with certainty that there are present in the tissues, enzymes that change dextrose to glycogen and _vice versa_, that break down and build up the proteids, and that aid in the oxidations at the cells. The necessity for such enzymes is quite apparent. *Summary.*—The digested nutrients are taken up by the capillaries and the lymph vessels and transferred by two routes to the circulation. In passing from the alimentary canal into the circulation the more important of the foods undergo changes which adapt them to the needs of the body. Since materials are absorbed more rapidly than they are used, means are provided for storing them and for supplying them to the cells as their needs require. _Capability of storage is an essential quality of energy-yielding foods_; and substances, such as alcohol, which lack this quality are not adapted to the needs of the body. For causing the chemical changes that occur in the storage of foods, as well as the oxidations at the cells, the presence of active agents, or enzymes, is necessary. *Exercises.*—1. In what respects does the absorption of food materials from the alimentary canal differ from the absorption of a simple liquid by a solid? 2. In what different ways is the small intestine especially adapted to the work of absorption? 3. What are the parts of a villus? What are the lacteals? Account for the name. 4. What part is played by the capillaries and the lacteals in the work of absorption? How does their work differ? 5. What changes, if any, take place in water, common salt, fat, proteids, and carbohydrates during absorption? 6. What double purpose is served by the processes of digestion? 7. Trace the passage of proteids, fats, and carbohydrates from the small intestine into the general circulation. 8. What is the necessity for storing nutrients in the body? Why is it not also necessary to store up oxygen? 9. In what form and at what places is each of the principal nutrients stored?