“In experiments made with rolled oats at the Minnesota Experiment Station, it appeared that cooking (four hours) did not make the starch much more soluble. However, it so changed the physical structure of the grains that a given amount of digestive ferment could render much more of it soluble in a given time than when it was cooked for only half an hour. “On the basis of the results obtained, the difficulty commonly experienced in digesting imperfectly cooked oatmeal was attributed to the large amounts of glutinous material which surrounds the starch grains and prevent their disintegration. When thoroughly cooked the protecting action of the mucilaginous protein is overcome, and the compound starch granules are sufficiently disintegrated to allow the digestive juices to act. In other words, the increased digestibility of the thoroughly cooked cereal is supposed to be largely due to a physical change in the carbohydrates, which renders them more susceptible to the action of digestive juices.” * * * * * =Pastry.= Pastry owes its harmful character to the interference of fat as shown on page 198, with the proper solution of the starch,—at least such pastry as requires the mixing of flour with fat; the coating of these granules with fat prevents them from coming in contact with liquids; the cells cannot absorb water, swell and burst so that they may dissolve. The fat does not furnish sufficient water for this and so coats the starch granules as to prevent the absorption of water in mixing, or of the saliva in mastication. This coating of fat is not relieved until late in the process of digestion, or until the food reaches the intestines. This same objection applies to rich gravies, unless the flour be dissolved in water and heated before being mixed with the fats. The objection, therefore, is to such pastry as is made by mixing flour with fat, as in pie crust; it does not apply to most puddings. Heat, in cooking, causes a combustion of the carbonic acid gas and the effort of this gas to escape, as well as the steam occasioned by the water in the food, causes the bubbles. When beaten eggs are used, the albuminoids in the bubbles expand the walls, which stiffen with the heat and cause the substances containing eggs to be porous. * * * * * [Sidenote: Cooking of Vegetables] Since the root vegetables contain a large proportion of carbohydrates, they should be well cooked, in order that the cells may be fully dissolved, and the crude fibre broken. Vegetables are best cooked in soft water, as lime or magnesia, the chemical ingredients which make water “hard”, make the vegetables less soluble. Vegetables and fruits become contaminated with the eggs of numerous parasites from the fertilizers used; hence they should be thoroughly washed.