Ages ago, when we were amoebæ or little drops of protoplasm, we had no eyes or nose or separate stomach for digesting food. The one little cell body did everything. One of the most important powers of that cell body was its power of digesting and assimilating food, and its most important food was the nitrogenous food or protein from which it built up its own body substance. Now, foreign or food protein cannot be simply absorbed as such. Foreign protein is a poison and never tolerated in the blood. The foreign protein used as food must first be changed into the special kind of protein that the body can use. The foreign protein is changed by splitting its molecule into its simplest parts and then recombining them in the desired form. The complex protein molecule, containing those sixty atoms of carbon that gave the Schrecklichkeit to the German professor of chemistry as related on page 71, is split up again and again into simpler forms. The end products are harmless, but the early splittings produce both poisonous and non-poisonous products. The end-results of these successive splittings, the splinters, as it were, are then combined by the amoeba to form its own kind of protein or body substance. As we rose in the animal scale, instead of being an amoeba of a single cell, we became constructed of millions of tiny cells and began to set aside certain groups of cells to do special work, the eyes for seeing, the ears for hearing, the lungs for breathing, the digestive organs to prepare our food and a sheath of harder cells over the outside of the body that we call our skin and mucous membranes. Specialized as those cells have been for many generations, they have never forgotten that a foreign protein is a food or, perhaps, an enemy, to be split up and decomposed at sight. So, the epithelial cells of the mucous membrane of the nose and eyes, though they have no longer anything to do with digesting our food, secrete a ferment or enzyme that can split up any protein that may happen along. This process is called _parenteral digestion_ or digestion outside of the intestines; and this theory of the parenteral digestion of protein is the foundation of the anaphylaxis theory of hay fever. During the growing months of the year the air is full of pollen that is blown in everybody's eyes and nose. In that pollen is a proteid that is digested by the secretion of those mucous membranes, proceeding exactly as food is digested in the stomach and intestines, splitting up the complex proteid molecule into simpler groups, and forming both poisonous and non-poisonous substances. In the normal eyes and nose this splitting of the protein proceeds slowly, forming only minute amounts of poison. As absorption from the eyes and nose is slight, no unpleasant effects are produced.