*To illustrate the Action of the Gastric Juice.*—Add to a tumbler two thirds full of water as much scale pepsin (obtained from a drug store) as will stay on the end of the large blade of a penknife. Then add enough hydrochloric acid to give a slightly sour taste. Place in the artificial gastric juice thus prepared some boiled white of egg which has been finely divided by pressing it through a piece of wire gauze. Also drop in a single large lump. Keep in a warm place (about the temperature of the body) for several hours or a day, examining from time to time. What is the general effect of the artificial gastric juice upon the egg? *To illustrate Effect of Alcohol upon Gastric Digestion.*—Prepare a tumbler half full of artificial gastric juice as in the above experiment, and add 10 cubic centimeters of this to each of six clean test tubes bearing labels. To five of the tubes add alcohol from a burette as follows: (1) .5 c.c., (2) 1 c.c., (3) 1.5 c.c., (4) 2 c.c., and (5) 3 c.c., leaving one tube without alcohol. Now add to each tube about 1/4 gram of finely divided white of egg from the experiment above, and place all of the tubes in a beaker half full of water. Keep the water a little above the temperature of the body for several hours, examining the tubes at intervals to note the progress of digestion. Inferences. CHAPTER XI - ABSORPTION, STORAGE, AND ASSIMILATION The dissolved nutrients, to reach the cells, must be transferred from the alimentary canal to the blood stream. This process is known as _absorption_. In general, absorption means the penetration of a liquid into the pores of a solid, and takes place according to the simple laws of molecular movements. The absorption of food is, however, not a simple process, and the passage takes place through an _active_ (living) membrane. Another difference is that certain foods undergo chemical change while being absorbed. *Small Intestine as an Organ of Absorption.*—While absorption may occur to a greater or less extent along the entire length of the alimentary canal, most of it takes place at the small intestine. Its great length, its small diameter, and its numerous blood vessels all adapt the small intestine to the work of absorption. The transverse folds in the mucous membrane, by retarding the food in its passage and by increasing the absorbing surface, also aid in the process. But of greatest importance are the minute elevations that cover the surface of the mucous membrane, known as *The Villi.*—Each single elevation, or villus, has a length of about one fiftieth of an inch and a diameter about half as great (_A_, Fig. 76), and contains the following essential parts: 1. An outer layer of epithelial cells, resting upon a connective tissue support. 2. A small lymph tube, called a _lacteal_, which occupies the center of the villus and connects at the base with other lymph tubes, also called lacteals (_B_, Fig. _76_). 3. A network of capillaries.