The pancreas is a secretive gland located entirely outside of the intestinal walls, and produces a juice which is poured into the small intestines at the point where the bile enters. Pancreatic juice is acidulous, and also strongly alkaline. As soon as the food, passing from the stomach, comes in contact with the pancreatic juice and the bile, the acid is neutralized, and the mass becomes alkaline. The pancreatic juice contains three important enzyms: 1 Amylopsin--acts on starch 2 Trypsin--acts on proteids 3 Steapsin--a fat-splitting enzym Pancreatic juice also has the power of coagulating milk, and is believed to contain some rennet. [Sidenote: Power of amylopsin] Amylopsin, the starch-digesting enzym, appears to be very similar to ptyalin in its power to digest carbohydrates. Amylopsin completes the digestion of starch that was begun by the saliva. It acts on starch with great activity. One part of amylopsin can change forty thousand times its bulk of starch to glucose. This can act only in an alkaline solution, and if any abnormal fermentation takes place in the digestive tract, producing a large quantity of acids, the digestion of starch is stopped. It is interesting to note that this enzym is entirely absent from the pancreatic juice of infants. This explains why infants cannot digest starch. [Sidenote: Comparison of trypsin and pepsin] The second enzym to be considered in the pancreatic juice is trypsin. This is a substance distinct from pepsin, but its action is the same. The chief distinction is that trypsin acts in an alkaline solution, while pepsin acts in an acid solution. Trypsin is much more energetic in its digestive power than the pepsin of the gastric juice. It completes the digestion of proteids that is begun in the stomach, and converts all proteids into soluble forms. A number of forms of proteid that are not acted on at all by the gastric juice are readily digested by the trypsin of the pancreatic juice. [Sidenote: Fat digestion and absorption] The fat-digesting enzym of the pancreatic juice is steapsin. This is the principal fat-digesting enzym of the body. This substance has power to split fats; that is, to convert them into fatty acids and glycerin of which they were originally composed. This fatty acid then combines with the alkalis of the bile and of the pancreatic juice to form soap. Soap is soluble, and passes through the walls of the small intestines in this form. Having passed through the walls of the intestines, soap is again changed into fat. The probable reason for which Nature adopts such a complex process for the absorption of fat, is because fat is insoluble. If the intestinal walls were so constructed that fat-globules could be taken directly through them, they would also be open for the entrance of germs and other foreign substances. [Sidenote: Frying fat unwholesome]